consequently.org: Greg Restall’s website in consequently.org: Greg Restall’s website Greg Restall's publications on logic and philosophyGreg RestallGreg Restallgreg@consequently.orgPhilosophy, Logic, mathematics, pdf, research, University, Greg Restall, Melbourne, Australia, VictorianoHugo
https://consequently.org/
en-usTue, 01 Oct 2019 22:44:39 UTCconsequently.org: Greg Restall’s website
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Mon, 01 Jan 0001 00:00:00 UTChttps://consequently.org/Presentations
https://consequently.org/presentation/
Mon, 01 Jan 0001 00:00:00 UTChttps://consequently.org/presentation/Assertions, Denials, Questions, Answers, and the Common Ground
https://consequently.org/presentation/2019/assertion-denial-qa-common-ground-arche/
Sun, 29 Sep 2019 00:00:00 UTChttps://consequently.org/presentation/2019/assertion-denial-qa-common-ground-arche/<p><em>Abstract</em>: In this talk, I examine some of the interconnections between norms governing assertion, denial, questions and answers, and the common ground of a discourse. When we pay attention to the structure of norms governing polar (yes/no) questions, we can clarify the distinction between strong and weak denials, together with the parallel distinction between strong and weak assertion, and the way that these speech acts interact with the common ground.</p>
<p>With those connections established, I respond to two criticisms of the program sketched out in my 2005 paper “Multiple Conclusions”. First, that understanding the upshot of a valid sequent <em>X</em> ⊢ <em>Y</em> as enjoining us to not assert each member of <em>X</em> and deny each member of <em>Y</em> is altogether too weak to explain the inferential force of logical validity. Deriving <em>X</em> ⊢ <em>A</em> should tell us, after all, something about justifying <em>A</em> on the basis of <em>X</em>, rather than merely prohibiting <em>A</em>’s denial. Where is the force to actually conclude the conclusion of a proof? A second, related criticism is that the format of multiple conclusion sequents seems unsatisfactory, in that it has no place for distinguishing a single conclusion, and proofs, after all, seem to be proofs of individual claims.</p>
<p>I will argue that both of these concerns can be assuaged if we pay closer attention to the norms connecting assertions and denials along with <em>justification requests</em> – questions aiming at eliciting reasons for assertions or denials. Once we understand the connection between justification requests, definitionsand the common ground, we will see not only that the these two concerns can be met. A derivation of a sequent <em>X</em> ⊢ <em>A</em>,<em>Y</em> gives us an answer to a justification request “why <em>A</em>?” in any available context where each member of <em>X</em> has been ruled in and each member of <em>Y</em> has been ruled out, and a derivation of a sequent <em>X</em>,<em>B</em> ⊢ <em>Y</em>, similarly gives us an answer to the justification request “why not <em>B</em>?” in any such context. The picture that results utilises the full multiple premise, multiple conclusion sequent calculus of classical logic, and does due justice to the idea that a proof (or a refutation) proves (or refutes) <em>one thing</em> relative to background assumptions or premises. In addition, when we consider the connection between justification requests and the norms governing <em>definitions</em>, we can see more clearly what could be involved in taking the connective/quantifier rules of a logical system to <em>define</em> the concepts they introduce.</p>
<ul>
<li><p>The talk is a presentation at the Metaphysics and Logic Group seminar at Arché at the University of St Andrews.</p></li>
<li><p>The <a href="https://consequently.org/slides/assertion-denial-qa-common-ground-slides-arche.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/assertion-denial-qa-common-ground-handout-arche.pdf">handout is here</a>.</p></li>
</ul>
Collection Frames for Substructural Logics
https://consequently.org/presentation/2019/collection-frames-lancog-lisbon/
Tue, 24 Sep 2019 00:00:00 UTChttps://consequently.org/presentation/2019/collection-frames-lancog-lisbon/<p><em>Abstract</em>: In this talk I present a new frame semantics for positive substructural and relevant propositional logics. This frame semantics is both a <em>generalisation</em> of Routley–Meyer ternary frames and a <em>simplification</em> of them. The key innovation is the use of a single accessibility relation to relate collections of points to points. Different logics are modelled by varying the kinds of collections featuring in the relation: for example, they can be sets, multisets, lists or trees. In this talk I will focus on multiset frames, which are sound and complete for the logic RW+ (positive multiplicative and additive linear logic with distribution for the additive connectives, or equivalently, the relevant logic R+ without contraction).</p>
<p>This is joint work with Shawn Standefer.</p>
<ul>
<li><p>The talk is a presentation at the <a href="http://cful.letras.ulisboa.pt/events/workshop-on-substructural-logics/">LanCog Workshop on Substructural Logics</a> at the Facultate de Letras at the University of Lisbon.</p></li>
<li><p>The <a href="https://consequently.org/slides/collection-frames-talk-lancog-lisbon.pdf">slides for the talk are available here</a>.</p></li>
</ul>
Classes
https://consequently.org/class/
Mon, 01 Jan 0001 00:00:00 UTChttps://consequently.org/class/PHIL40013: Uncertainty, Vagueness and Disagreement
https://consequently.org/class/2019/phil40013/
Wed, 24 Jul 2019 00:00:00 UTChttps://consequently.org/class/2019/phil40013/<p><strong><span class="caps">PHIL40013</span>: Uncertainty, Vagueness and Disagreement</strong> is a <a href="http://unimelb.edu.au">University of Melbourne</a> honours seminar subject for fourth-year students. Our aim in the Honours program is to introduce students to current work in research in philosophy of logic and language.</p>
<p>In 2019, we’re covering the connections between speech acts, epistemology and normative theory.</p>
<ol>
<li><strong>Introduction and overview, background</strong></li>
<li><strong>Speech acts: what are they?</strong>
<ul>
<li>J. L. Austin, <em>How to Do things with Words</em>, Clarendon Press,
Oxford, 1962. [<strong><em>Read Lecture 9</em></strong>]</li>
<li>H. P. Grice, “Logic and Conversation,” pages 41–58 in <em>Syntax and
Semantics</em>: <em>Speech Acts</em>, edited by P. Cole and J. L. Morgan,
Academic Press, New York, 1975.</li>
<li>Sarah E. Murray and William B. Starr, “<a href="http://dx.doi.org/10.1093/oso/9780198738831.003.0009">Force and Conversational States</a>,” pages 202–236 in <em>New Work on Speech Acts</em>, edited by Daniel Fogal, Daniel Harris and Matthew Moss, Oxford University Press, 2018. [<strong><em>Read Sections 9.1 and 9.2</em></strong>]</li>
<li>Nuel Belnap “<a href="http://dx.doi.org/10.1007/BF00368389">Declaratives are not Enough</a>”, <em>Philosophical Studies</em> 59:1 (1990) 1–30.</li>
<li>Mark Lance and Rebecca Kukla “<a href="http://dx.doi.org/10.1086/669565">Leave the Gun; Take the Cannoli! The Pragmatic Topography of Second-Person Calls</a>” <em>Ethics</em> 123:3 (2013) 456–478.</li>
<li>Mark Lance and Rebecca Kukla <em>Yo! and Lo! The Pragmatic Topography of the Space of Reasons,</em> Harvard University Press, 2009. [<strong><em>Read Chapter 1</em></strong>]</li>
<li>Craige Roberts “<a href="http://dx.doi.org/10.1093/oso/9780198738831.001.0001">Speech Acts in Discourse Context</a>”, pages 317–359 in <em>New Work on Speech Acts</em>, edited by Daniel Fogal, Daniel Harris and Matthew Moss, Oxford University Press, 2018.</li>
</ul></li>
<li><strong>Assertion</strong>
<ul>
<li>John Macfarlane, “<a href="http://dx.doi.org/10.1093/acprof:oso/9780199573004.001.0001">What is Assertion?</a>” pages 79–96 in <em>Assertion</em>:
<em>New Philosophical Essays</em>, edited by Jessica Brown and Herman
Cappelen, Oxford University Press, 2011.</li>
<li>Ishani Maitra, “<a href="http://dx.doi.org/10.1093/acprof:oso/9780199573004.001.0001">Assertion, Norms, and Games</a>” pages 277–296 in
<em>Assertion</em>: <em>New Philosophical Essays</em>, edited by Jessica Brown and
Herman Cappelen, Oxford University Press, 2011.</li>
<li>Jennifer Lackey, “<a href="http://dx.doi.org/10.1111/j.1468-0068.2007.00664.x">Norms of Assertion</a>,” <em>Noûs</em> 41:4 (2007) 594–626.</li>
<li>Rachel Mckinnon, <em>The Norms of Assertion</em>: <em>Truth, Lies, and Warrant,</em> Palgrave, 2015.</li>
<li>Peter Pagin, “<a href="http://plato.stanford.edu/archives/spr2015/entries/assertion/">Assertion</a>”, <em>The Stanford Encyclopedia of Philosophy,</em> 2015.</li>
</ul></li>
<li><strong>Common Ground and Accommodation</strong>
<ul>
<li>Robert Stalnaker, “<a href="http://dx.doi.org/10.1023/A:1020867916902">Common Ground</a>,” <em>Linguistics and Philosophy</em> 25:5–6 (2002) 701–721.</li>
<li>Mandy Simons, “<a href="http://dx.doi.org/10.1023/A:1023004203043">Presupposition and Accommodation: Understanding the Stalnakerian Picture</a>,” <em>Philosophical Studies</em> 112:3 (2003) 251–278.</li>
<li>Craige Roberts, “<a href="https://onlinelibrary-wiley-com/doi/pdf/10.1002/9781118398593.ch22">Accommodation in a Language Game</a>”, pages 345–366 in <em>A Companion to David Lewis</em>, edited by Barry Loewer and Jonathan Schaffer, John Wiley & Sons, Ltd., 2015.</li>
<li>David Lewis, “<a href="http://dx.doi.org/10.1007/BF00258436">Scorekeeping in a Language Game</a>”, <em>Journal of Philosophical Logic</em> 8:1 (1979) 339–359.</li>
<li>Paal Antonsen, “<a href="http://dx.doi.org/10.1093/analys/anx145">Scorekeeping</a>”, <em>Analysis</em> 78:4 (2018) 589–595.</li>
</ul></li>
<li><strong>Cooperation, Convention and Norms</strong>
<ul>
<li>Sarah E. Murray and William B. Starr, “<a href="http://dx.doi.org/10.1093/oso/9780198738831.003.0009">Force and Conversational States</a>,” pages 202–236 in <em>New Work on Speech Acts</em>, edited by Daniel Fogal, Daniel Harris and Matthew Moss, Oxford University Press, 2018. [<strong><em>Read Sections 9.3 to 9.5</em></strong>]</li>
<li>Cristina Bicchieri, <em>The Grammar of Society</em>: <em>the nature and dynamics of social norms</em>, Cambridge University Press, 2006. [<strong><em>Read Chapter 1</em></strong>]</li>
<li>Cristina Bicchieri, <a href="http://dx.doi.org/10.1093/acprof:oso/9780190622046.001.0001"><em>Norms in the Wild</em>: <em>how to diagnose, measure, and change social norms</em></a>, Oxford University Press, 2017.</li>
</ul></li>
<li><strong>Stereotypes and Generics</strong>
<ul>
<li>Sarah-Jane Leslie, “<a href="http://dx.doi.org/10.1111/j.1520-8583.2007.00138.x">Generics and the Structure of the Mind</a>,” <em>Philosophical Perspectives</em> 21:1 (2007) 375–403.</li>
<li>Sally Haslanger, “<a href="http://dx.doi.org/10.1007/978-90-481-3783-1_11">Ideology, Generics, and Common Ground</a>,” pages 179–207 in <em>Feminist Metaphysics</em>: <em>Explorations in the Ontology of Sex, Gender and the Self</em>, edited by Charlotte Witt, Springer, Dordrecht, 2011.</li>
<li>Rachel Katharine Sterken, “<a href="http://dx.doi.org/10.1111/phc3.12431">The Meaning of Generics</a>” <em>Philosophy Compass,</em> 12:8 (2017) e12431.</li>
<li>Jennifer Saul, “<a href="http://dx.doi.org/10.1080/0020174x.2017.1285995">Are Generics Especially Pernicious?</a>” <em>Inquiry,</em> advance access (2019), 1–18.</li>
</ul></li>
<li><strong>Authority and Epistemic Territory</strong>
<ul>
<li>Jennifer Nagel, “<a href="http://dx.doi.org/10.1017/epi.2015.4">The Social Value of Reasoning in Epistemic
Justification</a>,” <em>Episteme</em> 12:2 (2015) 297–308.</li>
<li>John Heritage, “<a href="http://dx.doi.org/10.1080/08351813.2012.646684">Epistemics in Action: Action Formation and Territories of Knowledge</a>,” <em>Research on Language and Social Interaction</em> 45:1 (2012) 1–29.</li>
<li>Akio Kamio, <em>Territory of Information,</em> John Benjamins, 1997.</li>
<li>Hugo Mercier and Dan Sperber, “<a href="http://dx.doi.org/10.1017/s0140525x10000968">Why do Humans Reason? Arguments for an argumentative theory</a>,” <em>Behavioral and Brain Sciences</em> 34:2 (2011) 57–74.</li>
</ul></li>
<li><strong>Illocutionary Silencing</strong>
<ul>
<li>Rae Langton, “<a href="https://www-jstor-org/stable/2265469">Speech Acts and Unspeakable Acts</a>,” <em>Philosophy</em> & <em>Public Affairs</em> 22:4 (1993) 293–330.</li>
<li>Ishani Maitra, “<a href="https://www-jstor-org/stable/27822050">Silencing Speech</a>,” <em>Canadian Journal of Philosophy</em> 39:2 (2009) 309–338.</li>
<li>Alessandra Tanesini, “<a href="http://aristoteliansupp.oxfordjournals.org/content/90/1/71">“Calm Down, Dear”: Intellectual Arrogance,
Silencing and Ignorance</a>,” <em>Aristotelian Society Supplementary Volume</em> 90:1 (2016) 71–92.</li>
<li>Alexander Bird, “<a href="https://doi-org/10.1111/1468-0114.00137">Illocutionary Silencing</a>,” <em>Pacific Philosophical Quarterly</em> 83:1 (2002) 1–15.</li>
<li>Mari Mikkola, “<a href="http://dx.doi.org/10.1111/j.1468-0114.2011.01404.x">Illocution, Silencing and the Act of Refusal</a>,” <em>Pacific Philosophical Quarterly</em> 92:3 (2011) 415–437.</li>
<li>Kristie Dotson, “<a href="http://dx.doi.org/10.1111/j.1527-2001.2011.01177.x">Tracking Epistemic Violence, Tracking Practices of Silencing</a>,” <em>Hypatia</em> 26:2 (2011) 236–257.</li>
</ul></li>
<li><strong>Gaslighting</strong>
<ul>
<li>Kate Abramson, “<a href="http://dx.doi.org/10.1111/phpe.12046">Turning up the Lights on Gaslighting</a>,” <em>Philosophical Perspectives</em> 28:1 (2014) 1–30.</li>
<li>Kate Manne, <a href="http://dx.doi.org/10.1093/oso/9780190604981.001.0001"><em>Down Girl</em>: <em>the logic of misogyny</em></a>, Oxford
Univeristy Press, 2018. [<strong><em>Read Chapter 1</em></strong>]</li>
<li>Andrew D. Spear, “<a href="http://dx.doi.org/10.1007/s11245-018-9611-z">Gaslighting, Confabulation, and Epistemic
Innocence</a>,” <em>Topoi</em> early access (2018).</li>
<li>Cynthia A. Stark, “<a href="http://dx.doi.org/10.1093/monist/onz007">Gaslighting, Misogyny, and Psychological
Oppression</a>,” <em>The Monist</em> 102:2 (2019) 221–235.</li>
</ul></li>
</ol>
<p>For further information, contact me. To participate, check <a href="https://handbook.unimelb.edu.au/view/2019/PHIL40013">the handbook</a>.</p>
PHIL20030: Meaning, Possibility and Paradox
https://consequently.org/class/2019/phil20030/
Wed, 24 Jul 2019 00:00:00 UTChttps://consequently.org/class/2019/phil20030/
<p><strong><span class="caps">PHIL20030</span>: Meaning, Possibility and Paradox</strong> is a <a href="http://unimelb.edu.au">University of Melbourne</a> undergraduate subject introducing logic to philosophy students. It’s taught by <a href="http://consequently.org">Greg Restall</a> and <a href="https://shawn-standefer.github.io">Shawn Standefer</a>.</p>
<p>This year, we have completely revised our curriculum. Now the subject introduces the proof theory and model theory of propositional, modal and predicate logic–in that order. We’re writing an introductory text <em>Logical Methods</em>, which we’re trialling with this class, as well as producing explanatory videos to use along with the text.</p>
<p>Here’s the outline of the subject.</p>
<h3 id="preliminaries">Preliminaries</h3>
<ul>
<li>Introduction
<ul>
<li>Arguments and Trees</li>
<li>Sentences and Formulas</li>
</ul></li>
</ul>
<h3 id="propositional-logic">Propositional Logic</h3>
<ul>
<li>Connectives: and & if
<ul>
<li>Conjunction</li>
<li>Conditional</li>
<li>Biconditional</li>
</ul></li>
<li>More connectives: not & or
<ul>
<li>Negation and falsum</li>
<li>Disjunction</li>
<li>Our System of Proofs</li>
</ul></li>
<li>Facts about proofs & provability
<ul>
<li>Facts about provability</li>
<li>Normalisation</li>
<li>The Subformula Property</li>
<li>Consequences of Normalisation</li>
</ul></li>
<li>Models & counterexamples
<ul>
<li>Models and truth tables</li>
<li>Counterexamples and validity</li>
<li>Model-theoretic validity</li>
</ul></li>
<li>Soundness & completeness
<ul>
<li>Soundness</li>
<li>Completeness</li>
<li>Proofs first or models first?</li>
<li>Heyting algebras</li>
</ul></li>
</ul>
<h3 id="modal-logic">Modal Logic</h3>
<ul>
<li>Necessity & possibility
<ul>
<li>Possible worlds models</li>
<li>Validity</li>
<li>Strict conditionals and ambiguities</li>
<li>Propositions</li>
<li>Another notion of necessity</li>
<li>Equivalence relations and epistemic logic</li>
</ul></li>
<li>Actuality & two-dimensional logic
<ul>
<li>Actuality models and double indexing</li>
<li>Validity</li>
<li>Fixity and diagonal propositions</li>
<li>Real world validity</li>
</ul></li>
<li>Natural deduction for modal logics
<ul>
<li>Natural deduction for S4</li>
<li>Natural deduction for S5</li>
<li>Features of S5</li>
</ul></li>
</ul>
<h3 id="predicate-logic">Predicate Logic</h3>
<ul>
<li>Quantifiers
<ul>
<li>Syntax</li>
<li>Natural deduction for CQ</li>
<li>What is provable?</li>
<li>Generality and eliminating detours</li>
</ul></li>
<li>Models for first-order logic
<ul>
<li>Models and assignments of values</li>
<li>Substitution</li>
<li>Counterexamples and validity</li>
<li>Compactness and what this means</li>
</ul></li>
</ul>
<p>One novelty in our approach to the subject is the balance between proof theory and model theory. We introduce propositional logic by way of Gentzen/Prawitz-style natural deduction—for intuitionistic logic—and along the way, each time we introduce the rules for a connective, we show that they are in harmony. So, it’s not too hard to show that proofs in the whole system can be normalised and we get the subformula property for normal proofs. (So, we can gesture in the direction of provability being <em>analytic</em> in a strong sense, since a normal proof literally <em>analyses</em> the premises and conclusion into components and connects them using the fundamental rules governing the concepts involved.)</p>
<p>Once that’s done, we then introduce Boolean valuations (and truth tables), and we can show that the proof system is sound but not complete for validity defined as the absence of a Boolean counterexample. Approaching things this way means we have an interesting discussion about soundness and completeness, and about intuitionistic and classical logic, and whether we should be happy with the gap between proofs and models or not, and if not, whether we should close that gap by adding to our proof system (that way lies <em>classical</em> natural deduction), or whether we should close the gap by enriching our class of models to serve as counterexamples (here we sketch Heyting algebras, as generalisations of Boolean valuations, but we point to Kripke models, too). There’s also scope for a discussion of whether we should understand logic in a proof-first way or a model-first way (or both, or neither), and how proofs and models relate to however it is that words and concepts get their meanings.</p>
<p>With that done, we’re halfway through the subject. Having arrived at Boolean valuations, it’s a short hop, skip and jump to Carnap’s models for modality, and their generalisation, universal models for the modal logic S5. So, we look at these models for possibility and necessity, and show how these possible worlds models can be used to analyse modality, strict conditionality, and similar notions.</p>
<p>Then with models like these we can be of service to our colleagues by introducing double-indexing and two-dimensional modal logic, and the analysis of fixedly diagonal propositions, and the relationship between analyticity, necessity and <em>a priority</em>.</p>
<p>With these model-theoretic considerations in hand, we turn to the question of what it might be to <em>derive</em> a modal claim, and we turn to the natural deduction rules for modals, which introduce constraints on assumptions. One way to prove that \(A\) is necessary, after all, is to prove \(A\) from claims of the form \(\Box B\), for those claims hold not only <em>here</em>, but also in any alternate circumstances, too. So, we get natural deduction systems for S4 and S5 rather straightforwardly.</p>
<p>Proving something more <em>general</em> than \(A\) by proving \(A\) from premises satisfying certain conditions sounds familiar if you’ve dealt with <em>quantifiers</em> before. How to you show that <em>everything</em> is an \(F\)? By proving that \(Fa\) when we have assumed <em>nothing about \(a\)</em>. Then our proof applies <em>no matter what \(a\) is</em>. So, we can generalise the conditions for modal proof to proofs with <em>quantifiers</em> too. So, we introduce the logic of first-order quantifiers with natural deduction first, and once we’ve done that, we turn back to models at last.</p>
<p>So, the introduction to logic has a rhythm, taking us from proofs to models of propositional logic, through models and then proofs for modal logic, and then to proofs and models for predicate logic. Along the way we look at issues in the philosophy of logic and the applications of logic to different issues in philosophy.</p>
<p>Although this curriculum and the course material is all ours, we are indebted to our colleagues for many discussions concerning the pedagogy of logic. I’ll single out two here. Allen Hazen talked to GR for many years about the pedagogical virtues of introducing modal logic before predicate logic to philosophy students. And <a href="http://davewripley.rocks">Dave Ripley</a> has, for the last couple of years, introduced logic using intuitionistic natural deduction and classical truth tables, making a virtue out of the soundness and <em>in</em>completeness of the pairing between the proof theory and the model theory. Neither Allen nor Dave would teach things how we have, but we’ve valued talking over the pedagogy with them over the years.</p>
<p>If you’d like to compare your mastery of logic, in comparison to what our students are learning, you can try your own hand at our <a href="https://consequently.org/resources/PHIL20030-2019-class-tasks-1-6.pdf">in-class tasks for weeks 1 to 6</a>.</p>
Assertions, Denials, Questions, Answers, and the Common Ground
https://consequently.org/presentation/2019/assertion-denial-qa-common-ground-express/
Thu, 13 Jun 2019 00:00:00 UTChttps://consequently.org/presentation/2019/assertion-denial-qa-common-ground-express/<p><em>Abstract</em>: In this talk, I examine some of the interconnections between norms governing assertion, denial, questions and answers, and the common ground of a discourse. When we pay attention to the structure of norms governing polar (yes/no) questions, we can clarify the distinction between strong and weak denials, together with the parallel distinction between strong and weak assertion, and the way that these speech acts interact with the common ground.</p>
<p>With those connections established, I respond to two criticisms of the program sketched out in my 2005 paper “Multiple Conclusions”. First, that understanding the upshot of a valid sequent <em>X</em> ⊢ <em>Y</em> as enjoining us to not assert each member of <em>X</em> and deny each member of <em>Y</em> is altogether too weak to explain the inferential force of logical validity. Deriving <em>X</em> ⊢ <em>A</em> should tell us, after all, something about justifying <em>A</em> on the basis of <em>X</em>, rather than merely prohibiting <em>A</em>’s denial. Where is the force to actually conclude the conclusion of a proof? A second, related criticism is that the format of multiple conclusion sequents seems unsatisfactory, in that it has no place for distinguishing a single conclusion, and proofs, after all, seem to be proofs of individual claims.</p>
<p>I will argue that both of these concerns can be assuaged if we pay closer attention to the norms connecting assertions and denials along with <em>justification requests</em> — questions aiming at eliciting reasons for assertions or denials. Once we understand the connection between justification requests, definitionsand the common ground, we will see not only that the these two concerns can be met. A derivation of a sequent <em>X</em> ⊢ <em>A</em>,<em>Y</em> gives us an answer to a justification request “why <em>A</em>?” in any available context where each member of <em>X</em> has been ruled in and each member of <em>Y</em> has been ruled out, and a derivation of a sequent <em>X</em>,<em>B</em> ⊢ <em>Y</em>, similarly gives us an answer to the justification request “why not <em>B</em>?” in any such context. The picture that results utilises the full multiple premise, multiple conclusion sequent calculus of classical logic, and does due justice to the idea that a proof (or a refutation) proves (or refutes) <em>one thing</em> relative to background assumptions or premises. In addition, when we consider the connection between justification requests and the norms governing <em>definitions</em>, we can see more clearly what could be involved in taking the connective/quantifier rules of a logical system to <em>define</em> the concepts they introduce.</p>
<ul>
<li><p>The talk is an invited address at the <a href="https://inferentialexpressivism.com/workshop/">Workshop on Bilateral Approches to Meaning</a>, at the University of Amsterdam.</p></li>
<li><p>The <a href="https://consequently.org/slides/assertion-denial-qa-common-ground-slides-express.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/assertion-denial-qa-common-ground-handout-express.pdf">handout is here</a>.</p></li>
</ul>
Assertions, Denials, Questions, Answers, and the Common Ground
https://consequently.org/presentation/2019/assertion-denial-qa-common-ground-mcmp/
Thu, 13 Jun 2019 00:00:00 UTChttps://consequently.org/presentation/2019/assertion-denial-qa-common-ground-mcmp/<p><em>Abstract</em>: In this talk, I examine interconnections between norms governing assertion, denial, questions and answers, and the common ground of a discourse. When we pay attention to the structure of norms governing polar (yes/no) questions, we can clarify the distinction between strong and weak denials, together with the parallel distinction between strong and weak assertion, and the way that these speech acts interact with the common ground.</p>
<p>With those connections established, I respond to two criticisms of the program sketched out in my 2005 paper “Multiple Conclusions”. First, that understanding the upshot of a valid sequent <em>X</em> ⊢ <em>Y</em> as enjoining us to not assert each member of <em>X</em> and deny each member of <em>Y</em> is altogether too weak to explain the inferential force of logical validity. Deriving <em>X</em> ⊢ <em>A</em> should tell us, after all, something about justifying <em>A</em> on the basis of <em>X</em>, rather than merely prohibiting <em>A</em>’s denial. Where is the force to actually conclude the conclusion of a proof? A second, related criticism is that the format of multiple conclusion sequents seems unsatisfactory, in that it has no place for distinguishing a single conclusion, and proofs, after all, seem to be proofs of individual claims.</p>
<p>I will argue that both of these concerns can be assuaged if we pay closer attention to the norms connecting assertions and denials along with <em>justification requests</em> — questions aiming at eliciting reasons for assertions or denials. Once we understand the connection between justification requests, definitionsand the common ground, we will see not only that the these two concerns can be met. A derivation of a sequent <em>X</em> ⊢ <em>A</em>,<em>Y</em> gives us an answer to a justification request “why <em>A</em>?” in any available context where each member of <em>X</em> has been ruled in and each member of <em>Y</em> has been ruled out, and a derivation of a sequent <em>X</em>,<em>B</em> ⊢ <em>Y</em>, similarly gives us an answer to the justification request “why not <em>B</em>?” in any such context. The picture that results utilises the full multiple premise, multiple conclusion sequent calculus of classical logic, and does due justice to the idea that a proof (or a refutation) proves (or refutes) <em>one thing</em> relative to background assumptions or premises. In addition, when we consider the connection between justification requests and the norms governing <em>definitions</em>, we can see more clearly what could be involved in taking the connective/quantifier rules of a logical system to <em>define</em> the concepts they introduce.</p>
<ul>
<li><p>The talk is a <a href="https://www.mcmp.philosophie.uni-muenchen.de/events_this-_week/restall_20190618/index.html">Seminar at the Munich Centre for Mathematical Philosophy</a>.</p></li>
<li><p>The <a href="https://consequently.org/slides/assertion-denial-qa-common-ground-slides-mcmp.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/assertion-denial-qa-common-ground-handout-mcmp.pdf">handout is here</a>.</p></li>
</ul>
Assertions, Denials, Questions, Answers, and the Common Ground
https://consequently.org/presentation/2019/assertion-denial-qa-common-ground-logicmelb/
Thu, 06 Jun 2019 00:00:00 UTChttps://consequently.org/presentation/2019/assertion-denial-qa-common-ground-logicmelb/<p><em>Abstract</em>: In this talk, I examine some of the interconnections between norms governing assertion, denial, questions and answers, and the common ground of a discourse. When we pay attention to the structure of norms governing polar (yes/no) questions, we can clarify the distinction between strong and weak denials, together with the parallel distinction between strong and weak assertion, and the way that these speech acts interact with the common ground.</p>
<p>With those connections established, I respond to two criticisms of the program sketched out in my 2005 paper “Multiple Conclusions”. First, that understanding the upshot of a valid sequent <em>X</em> ⊢ <em>Y</em> as enjoining us to not assert each member of <em>X</em> and deny each member of <em>Y</em> is altogether too weak to explain the inferential force of logical validity. Deriving <em>X</em> ⊢ <em>A</em> should tell us, after all, something about justifying <em>A</em> on the basis of <em>X</em>, rather than merely prohibiting <em>A</em>’s denial. Where is the force to actually conclude the conclusion of a proof? A second, related criticism is that the format of multiple conclusion sequents seems unsatisfactory, in that it has no place for distinguishing a single conclusion, and proofs, after all, seem to be proofs of individual claims.</p>
<p>I will argue that both of these concerns can be assuaged if we pay closer attention to the norms connecting assertions and denials along with <em>justification requests</em> — questions aiming at eliciting reasons for assertions or denials. Once we understand the connection between justification requests, definitionsand the common ground, we will see not only that the these two concerns can be met. A derivation of a sequent <em>X</em> ⊢ <em>A</em>,<em>Y</em> gives us an answer to a justification request “why <em>A</em>?” in any available context where each member of <em>X</em> has been ruled in and each member of <em>Y</em> has been ruled out, and a derivation of a sequent <em>X</em>,<em>B</em> ⊢ <em>Y</em>, similarly gives us an answer to the justification request “why not <em>B</em>?” in any such context. The picture that results utilises the full multiple premise, multiple conclusion sequent calculus of classical logic, and does due justice to the idea that a proof (or a refutation) proves (or refutes) <em>one thing</em> relative to background assumptions or premises. In addition, when we consider the connection between justification requests and the norms governing <em>definitions</em>, we can see more clearly what could be involved in taking the connective/quantifier rules of a logical system to <em>define</em> the concepts they introduce.</p>
<ul>
<li><p>The talk is a <a href="https://philevents.org/event/show/73102">Melbourne Logic Seminar</a>.</p></li>
<li><p>The <a href="https://consequently.org/slides/assertion-denial-qa-common-ground-slides-logicmelb.pdf">slides for the talk are available here</a>.</p></li>
</ul>
Writings
https://consequently.org/writing/
Mon, 01 Jan 0001 00:00:00 UTChttps://consequently.org/writing/Proofs and Models in Naive Property Theory: A Response to Hartry Field's “Properties, Propositions and Conditionals”
https://consequently.org/writing/proofs-and-models-in-npt/
Tue, 02 Apr 2019 00:00:00 UTChttps://consequently.org/writing/proofs-and-models-in-npt/<p>In our response Field’s “Properties, Propositions and Conditionals”, we explore the methodology of Field’s program. We begin by contrasting it with a proof-theoretic approach and then commenting on some of the particular choices made in the development of Field’s theory. Then, we look at issues of property identity in connection with different notions of equivalence. We close with some comments relating our discussion to Field’s response to Restall’s “<a href="https://consequently.org/writing/stp/">What are we to accept, and what are we to reject, when saving truth from paradox?</a>”.</p>
Isomorphisms in a Category of Proofs
https://consequently.org/presentation/2019/isomorphisms-pts3/
Thu, 07 Mar 2019 00:00:00 UTChttps://consequently.org/presentation/2019/isomorphisms-pts3/<p><em>Abstract</em>: In this talk, I show how a category of classical proofs can give rise to three different hyperintensional notions of sameness of content. One of these notions is very fine-grained, going so far as to distinguish \(p\) and \(p\land p\), while identifying other distinct pairs of formulas, such as \(p\land q\) and \(q\land p\); \(p\) and \(\neg\neg p\); or \(\neg(p\land q)\) and \(\neg p\lor\neg q\). Another relation is more coarsely grained, and gives the same account of identity of content as equivalence in Angell’s logic of analytic containment. A third notion of sameness of content is defined, which is intermediate between Angell’s and Parry’s logics of analytic containment. Along the way, we show how purely classical proof theory gives resources to define hyperintensional distinctions thought to be the domain of properly non-classical logics.</p>
<ul>
<li>This is a talk at the <a href="http://ls.informatik.uni-tuebingen.de/PTS3/overview.html">Third Tübingen Conference on Proof-Theoretic Semantics</a>, 27–30 March 2019.</li>
<li>The slides are <a href="https://consequently.org/slides/isomorphisms-talk-tubingen-2019.pdf">available here</a>, while a handout <a href="https://consequently.org/handouts/isomorphisms-handout-tubingen-2019.pdf">is here</a>.</li>
</ul>
Collection Frames for Substructural Logics
https://consequently.org/presentation/2019/collection-frames-logicmelb/
Thu, 07 Mar 2019 00:00:00 UTChttps://consequently.org/presentation/2019/collection-frames-logicmelb/<p><em>Abstract</em>: In this talk I present a new frame semantics for positive substructural and relevant propositional logics. This frame semantics is both a <em>generalisation</em> of Routley–Meyer ternary frames and a <em>simplification</em> of them. The key innovation is the use of a single accessibility relation to relate collections of points to points. Different logics are modelled by varying the kinds of collections featuring in the relation: for example, they can be sets, multisets, lists or trees. In this talk I will focus on multiset frames, which are sound and complete for the logic RW+ (positive multiplicative and additive linear logic with distribution for the additive connectives, or equivalently, the relevant logic R+ without contraction).</p>
<p>This is joint work with Shawn Standefer.</p>
<ul>
<li><p>The talk is a <a href="https://philevents.org/event/show/69618">Melbourne Logic Seminar</a>.</p></li>
<li><p>The <a href="https://consequently.org/slides/collection-frames-talk-logicmelb.pdf">slides for the talk are available here</a>.</p></li>
</ul>
PHIL30043: The Power and Limits of Logic
https://consequently.org/class/2019/phil30043/
Sat, 02 Mar 2019 00:00:00 UTChttps://consequently.org/class/2019/phil30043/
<p><strong><span class="caps">PHIL30043</span>: The Power and Limits of Logic</strong> is a <a href="https://handbook.unimelb.edu.au/view/2019/PHIL30043">University of Melbourne undergraduate subject</a>. It covers the metatheory of classical first order predicate logic, beginning at the <em>Soundness</em> and <em>Completeness</em> Theorems (proved not once but <em>twice</em>, first for a tableaux proof system for predicate logic, then a Hilbert proof system), through the <em>Deduction Theorem</em>, <em>Compactness</em>, <em>Cantor’s Theorem</em>, the <em>Downward Löwenheim–Skolem Theorem</em>, <em>Recursive Functions</em>, <em>Register Machines</em>, <em>Representability</em> and ending up at <em>Gödel’s Incompleteness Theorems</em> and <em>Löb’s Theorem</em>.</p>
<figure>
<img src="https://consequently.org/images/godel.jpg" alt="Kurt Godel, seated">
<figcaption>Kurt Gödel, seated</figcaption>
</figure>
<p>The subject is taught to University of Melbourne undergraduate students (for Arts students as a part of the Philosophy major, for non-Arts students, as a breadth subject). Details for enrolment are <a href="https://handbook.unimelb.edu.au/view/2018/PHIL30043">here</a>. I make use of video lectures I have made <a href="http://vimeo.com/album/2262409">freely available on Vimeo</a>.</p>
<h3 id="outline">Outline</h3>
<p>The course is divided into four major sections and a short prelude. Here is a list of all of the videos, in case you’d like to follow along with the content.</p>
<h4 id="prelude">Prelude</h4>
<ul>
<li><a href="http://vimeo.com/album/2262409/video/59401942">Logical Equivalence</a></li>
<li><a href="http://vimeo.com/album/2262409/video/59403292">Disjunctive Normal Form</a></li>
<li><a href="http://vimeo.com/album/2262409/video/59403535">Why DNF Works</a></li>
<li><a href="http://vimeo.com/album/2262409/video/59463569">Prenex Normal Form</a></li>
<li><a href="http://vimeo.com/album/2262409/video/59466141">Models for Predicate Logic</a></li>
<li><a href="http://vimeo.com/album/2262409/video/59880539">Trees for Predicate Logic</a></li>
</ul>
<h4 id="completeness">Completeness</h4>
<ul>
<li><a href="http://vimeo.com/album/2262409/video/59883806">Introducing Soundness and Completeness</a></li>
<li><a href="http://vimeo.com/album/2262409/video/60249309">Soundness for Tree Proofs</a></li>
<li><a href="http://vimeo.com/album/2262409/video/60250515">Completeness for Tree Proofs</a></li>
<li><a href="http://vimeo.com/album/2262409/video/61677028">Hilbert Proofs for Propositional Logic</a></li>
<li><a href="http://vimeo.com/album/2262409/video/61685762">Conditional Proof</a></li>
<li><a href="http://vimeo.com/album/2262409/video/62221512">Hilbert Proofs for Predicate Logic</a></li>
<li><a href="http://vimeo.com/album/2262409/video/103720089">Theories</a></li>
<li><a href="http://vimeo.com/album/2262409/video/103757399">Soundness and Completeness for Hilbert Proofs for Predicate Logic</a></li>
</ul>
<h4 id="compactness">Compactness</h4>
<ul>
<li><a href="http://vimeo.com/album/2262409/video/63454250">Counting Sets</a></li>
<li><a href="http://vimeo.com/album/2262409/video/63454732">Diagonalisation</a></li>
<li><a href="http://vimeo.com/album/2262409/video/63454732">Compactness</a></li>
<li><a href="http://vimeo.com/album/2262409/video/63455121">Non-Standard Models</a></li>
<li><a href="http://vimeo.com/album/2262409/video/63462354">Inexpressibility of Finitude</a></li>
<li><a href="http://vimeo.com/album/2262409/video/63462519">Downward Löwenheim–Skolem Theorem</a></li>
</ul>
<h4 id="computability">Computability</h4>
<ul>
<li><a href="http://vimeo.com/album/2262409/video/64162062">Functions</a></li>
<li><a href="http://vimeo.com/album/2262409/video/64167354">Register Machines</a></li>
<li><a href="http://vimeo.com/album/2262409/video/64207986">Recursive Functions</a></li>
<li><a href="http://vimeo.com/album/2262409/video/64435763">Register Machine computable functions are Recursive</a></li>
<li><a href="http://vimeo.com/album/2262409/video/64604717">The Uncomputable</a></li>
</ul>
<h4 id="undecidability-and-incompleteness">Undecidability and Incompleteness</h4>
<ul>
<li><a href="http://vimeo.com/album/2262409/video/65382456">Deductively Defined Theories</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65392670">The Finite Model Property</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65393543">Completeness</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65440901">Introducing Robinson’s Arithmetic</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65442289">Induction and Peano Arithmetic</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65443650">Representing Functions and Sets</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65483655">Gödel Numbering and Diagonalisation</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65497886">Q (and any consistent extension of Q) is undecidable, and incomplete if it’s deductively defined</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65498016">First Order Predicate Logic is Undecidable</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65501745">True Arithmetic is not Deductively Defined</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65505372">If Con(PA) then PA doesn’t prove Con(PA)</a></li>
</ul>
UNIB10002: Logic, Language and Information
https://consequently.org/class/2019/unib10002/
Sat, 02 Mar 2019 00:00:00 UTChttps://consequently.org/class/2019/unib10002/<p><strong><span class="caps">UNIB10002</span>: Logic, Language and Information</strong> is a <a href="http://unimelb.edu.au">University of Melbourne</a> undergraduate breadth subject, introducing logic and its applications to students from a wide range of disciplines in the Arts, Sciences and Engineering. I coordinate this subject with my colleague Dr. Jen Davoren, with help from Prof. Lesley Stirling (Linguistics), Dr. Peter Schachte (Computer Science) and Dr. Daniel Murfet (Mathematics).</p>
<p>The subject is taught to University of Melbourne undergraduate students. Details for enrolment are <a href="https://handbook.unimelb.edu.au/view/2019/UNIB10002">here</a>.</p>
Generality and Existence I: Quantification and Free Logic
https://consequently.org/writing/generality-and-existence-1/
Fri, 01 Mar 2019 00:00:00 UTChttps://consequently.org/writing/generality-and-existence-1/<p>In this paper, I motivate a cut free sequent calculus for classical logic with first order quantification, allowing for singular terms free of existential import. Along the way, I motivate a criterion for rules designed to answer Prior’s question about what distinguishes rules for logical concepts, like ‘conjunction’ from apparently similar rules for putative concepts like ‘tonk’, and I show that the rules for the quantifiers—and the existence predicate—satisfy that condition.</p>
Generality and Existence 2: Modality and Quantifiers
https://consequently.org/presentation/2019/generality-and-existence-2-apa/
Tue, 05 Feb 2019 00:00:00 UTChttps://consequently.org/presentation/2019/generality-and-existence-2-apa/<p><em>Abstract</em>: In this talk, I motivate and define a cut free sequent calculus for first order modal predicate logics, allowing for singular terms free of existential import. I show that the <em>cut</em> rule is admissible in the cut-free calculus, and explore the relationship between contingent ‘world-bound’ quantifiers and possibilist ‘world-undbound’ quantifiers in the system.</p>
<ul>
<li><p>This is a talk for the Association for Symbolic Logic at the Central Division meeting of the American Philosophical Association, at Denver, Colorado.</p></li>
<li><p>The <a href="https://consequently.org/slides/generality-and-existence-2-slides-apa-screen.pdf">slides for the talk are available here</a>, and a version formatted for printing, as a handout, is <a href="https://consequently.org/slides/generality-and-existence-2-slides-apa-print.pdf">available here</a>.</p></li>
</ul>
News
https://consequently.org/news/
Sun, 27 Jan 2019 20:49:05 +1100https://consequently.org/news/Summer Reading 2018-2019
https://consequently.org/news/2019/summer-reading-2018-2019/
Sun, 27 Jan 2019 20:49:05 +1100https://consequently.org/news/2019/summer-reading-2018-2019/<p>This summer break, I set aside some time to turn off my devices, unplug from the internet, and read some honest-to-goodness <em>books</em>. Some I received from friends and family as Christmas or Birthday gifts (thanks, Sharon, Zac, Neil!), and some I had accumulated on my “to-read” pile waiting for just the right time. Here are some short reviews of my summer reading pile, in case you’d like to follow along.</p>
<p></p>
<p><blockquote class="twitter-tweet" data-lang="en"><p lang="en" dir="ltr">Christmas and New Year reading (and reference). <a href="https://t.co/LKLFIbQKPM">pic.twitter.com/LKLFIbQKPM</a></p>— Greg Restall (@consequently) <a href="https://twitter.com/consequently/status/1078484355981414400?ref_src=twsrc%5Etfw">December 28, 2018</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script></p>
<hr />
<p>Haruki Murakami’s <a href="https://www.amazon.com/What-Talk-About-When-Running/dp/0307389839/consequentlyorg"><em>What I Talk About When I Talk About Running</em></a> is a delightful little book. It’s an enjoyable and personable mixture of <em>memoir</em> and <em>runners’ journal</em>. I’ve taken up running as a serious exercise practice in the last few years, and Murakami’s writing about his serious practice of long-distance running, and how he fits that in to the life of a writer was challenging and inspiring.</p>
<p>After reading it, I thought I could take my running practice more seriously, and I surprised myself by managing my first sub 5 minute-per-kilometre 10K run in the next week. Reading <em>What I Talk About When I Talk About Running</em> will remain with me for some time.</p>
<hr />
<p>Rowan Williams, the former Archbishop of Canterbury, is well known to be a reflective thinker, whose theological writing seriously engages with a range of theological traditions, but which also comes from a sustained contemplative practice. I don’t find Williams’ writing <em>easy</em>, but it’s always been rewarding when I’ve made the time to slow down and digest it. Williams’ new book <a href="https://www.amazon.com/Christ-Heart-Creation-Rowan-Williams/dp/1472945549/consequentlyorg"><em>Christ the Heart of Creation</em></a> is an attempt to revisit the classical doctrine of the incarnation in a new way: by focussing relentlessly on the idea that there is no competition between divine and creaturely action. According to Williams, too often we conceive of God as just another agent like any agent–except perhaps rather <em>Bigger</em>. (The metaphor is strained, but the relationship between a creature and God is more akin to the relationship between a fictional character and its author than between one character and another. Hermione stands to Harry in rather a different way than Hermione does to J. K. Rowling.) The way the Creator acts in creation is categorically distinct from the way a creature acts in creation. Williams examines different vocabulary used to give an account of the incarnation–from Augustine, the Chalcedonian Creed and Byzantine theologians Maximus the Confessor and John of Damascus, through Aquinas and Calvin to Barth and Bonhoeffer, with a sprinkling of Kierkegaard and Wittgenstein along the way, and always with care to the creature/creation distinction firmly on focus.</p>
<p>The result is a sympathetic recasting of traditional doctrines in a manner that breathes life into what may have seemed obsolete vocabulary. For Williams, incarnational vocabulary is a natural expression of a community attempting to articulate what they have encountered God doing in and through the human life of Jesus. The icing on the cake for me was Williams’ discussion of Paul’s “Body of Christ” language, which is, on this view, <em>much</em> more than a metaphor. This was a valuable read, well worth the time to digest slowly.</p>
<hr />
<p><a href="https://www.amazon.com/Zen-Doctrine-No-Mind/dp/0877281823/consequentlyorg"><em>The Zen Doctrine of No-Mind</em></a>, by D. T. Suzuki, is an exposition of the teaching of the Zen master Hui-neng (638–713). This book is an introduction to a debate in the early development of Zen Buddhism, a debate about sudden enlightenment and the doctrine of no-mind. I’d read some elementary expositions of Zen Buddhism before, but it was good to tackle a more extended work by the master D. T. Suzuki.</p>
<hr />
<p><a href="https://www.amazon.com/Return-Prodigal-Son-Story-Homecoming/dp/0385473079/consequentlyorg"><em>The Return of the Prodigal Son</em>: <em>A Story of Homecoming</em></a>, is a little book featuring reflections by Henri Nouwen, on a famous <a href="https://en.wikipedia.org/wiki/The_Return_of_the_Prodigal_Son_(Rembrandt)">painting by Rembrandt</a>. The painting depicting the return of the prodigal son, from Jesus’ parable (<a href="http://bible.oremus.org/?ql=415579440">Luke 15:11-32</a>). Nouwen reflects on the painting as he undergoes a significant turn in his life, departing his life as an academic in the US to live as a chaplain at Daybreak, a L’Arche community in Toronto.</p>
<p>The book is a thoughtful meditation on the painting, systematically taking three distinct perspectives, first identifying with the returning younger son, then identifying with the older son, and – at the end – reflecting on what it could mean to identify with the father in the parable.</p>
<hr />
<p><a href="https://www.amazon.com/MaddAddam-Trilogy-Margaret-Atwood/dp/0307455483/consequently"><em>MaddAddam</em></a>, by Margaret Atwood is the third novel and the conclusion of the dystopian (post-apocalyptic) <em>Oryx and Crake</em> trilogy. I’d read the <a href="https://www.amazon.com/gp/product/0385721676/consequentlyorg">first (<em>Oryx and Crake</em>)</a> and <a href="https://www.amazon.com/gp/product/0307455475/consequentlyorg">second (<em>The Year of the Flood</em>)</a> books of the trilogy years ago, and this had been sitting on my shelf for a couple of years. Now, with this summer, I finally had time to read it.</p>
<p>The books of the trilogy are set in and around the “waterless flood”, which swept away most of humanity in a genetically engineered disaster. There is a two-track narrative in <em>MaddAddam</em>, with one thread set before the flood, and the other, in its aftermath. In this book we learn more of Zeb and Adam, half-brothers who play very different roles in the world leading up to the flood and its immediate aftermath, and we learn more of the Crakers, the genetically engineered placid human-variants who Crake designed to replace us in the wake of the apocalypse. Atwood is perceptive when it comes to the different social roles religions can play in a world undergoing radical change. While Adam’s community of God’s Gardeners (think of a sect of environmentally-minded Quakers and you won’t go far wrong) are the central focus in <em>The Year of the Flood</em> (Book 2), in <em>MaddAddam</em> we hear from Adam and Zeb’s father, “The Rev”, who established the corporate friendly Church of PetrOleum: “My friends, as we all know, ‘oleum’ is the Latin word for oil. And indeed, oil is holy throughout the Bible! What else is used for the anointing of priests and prophets and kings? Oil!” As with <em>The Handmaid’s Tale</em>, religion can be co-opted into repression or exploitation, as much as it might be a force for liberation or conservation.</p>
<hr />
<p>Richard Prum’s <a href="https://www.amazon.com/Evolution-Beauty-Darwins-Forgotten-Theory/dp/0385537212/consequentlyorg"><em>The Evolution of Beauty</em></a> is a colourful account of the evolutionary dynamics of mate choice and the debate between adaptationists and non-adaptationists. What I enjoyed most in the book was the many examples of the variety of behaviours in the animal world–particularly in different bird species, but also in primates–and the insight into the distinct dynamics for selection and how different behaviours arise as a result of how mate selection takes place. There are many striking examples of different mating behaviour between bower birds on the one hand (where the selection of mates is basically up to the female bird–the males perform in their bowers and the females choose from among the males) and ducks (where the males choose and mate with females). The evolutionary dynamics are very different in each case, resulting in not only an incredible variety of different behaviours (in bower collecting, mating displays, plumage colouration, etc.), but also in the differences between species in which forced copulation occurs (common in ducks, for example) and those in which it is rare or nonexsitent (bower birds).</p>
<p>Without reading into the secondary literature, I can’t say much about the debate between adaptationists and non-adaptationists (as far as I can tell this turns on different ways “fitness” can be understood, and this turns out to be a pretty subtle matter), so I’m not going to judge on whether Prum is right about the side of the debate he lands on – but I <em>do</em> think that the book is very valuable as an introduction to the many and varied dynamics of mate selection and evolution among animal life, and the consequences that this might have for the evolution of the variety of behaviours among our primate cousins–including us. This was a delightful read.</p>
<hr />
<p>The last book in my pile was <em>not</em> like the others. Gozo Shioda’s <a href="https://www.amazon.com/Aikido-Complete-Techniques-Gozo-Shioda/dp/1568364857/consequentlyorg"><em>Aikido</em>: <em>The Complete Basic Techniques</em></a> is not the kind of book you read from cover to cover. It’s a reference book, that you dip in and out of as required. I’ve referred to it repeatedly to help me remember and understand techniques I’m learning in my Aikodo classes. It’s one of the definitive Yoshinkan Aikido texts, and in my couple of years of practice, I’m reaching the stage where I’ve begun to learn enough of the <em>very</em> basic things that I am beginning to get hints of where the practice goes from here. I’m finding that having written words and pictures does help me reflect on and remember what I’m learning in class, so I’ll be referring to this a great deal in the years ahead.</p>New Work for a (Formal) Theory of Grounds
https://consequently.org/presentation/2018/new-work-for-a-theory-of-grounds-logicmelb/
Fri, 07 Dec 2018 00:00:00 UTChttps://consequently.org/presentation/2018/new-work-for-a-theory-of-grounds-logicmelb/<p><em>Abstract</em>: In this talk, I provide two different models for a theory of grounds meeting the following desiderata:\(\def\yright{\succ}\)</p>
<ol>
<li><em>Grammar</em>: There are objects, which we call <em>grounds</em>, which can be grounds <em>for</em> propositions or grounds <em>against</em> propositions.</li>
<li><em>Derivation</em>: A derivation of a sequent \(X\yright A,Y\) gives us a systematic way to construct a ground <em>for</em> \(A\) out of grounds for each member of \(X\) and grounds against each member of \(Y\), and a derivation of a sequent \(X,A\yright Y\) gives us a systematic way to construct a ground <em>against</em> \(A\) out of grounds for each member of \(X\) and grounds against each member of \(Y\). So, a derivation of \(\yright A\) gives us a way to construct a ground for \(A\), and a derivation of \(A\yright\) gives us a way to construct a ground against \(A\).</li>
<li><em>Interpretation</em>: This theory can be interpreted in an <em>epistemic</em> sense, where grounds are our means to access the truth or falsity of a proposition, or a <em>metaphysical</em> sense, where grounds show how a proposition is made true by the world.</li>
<li><em>Grasp</em>: Grounds are the kinds of things we can <em>possess</em>.</li>
<li><em>Hyperintensionality</em>: Not every ground is a ground for every tautology. A ground for \(A\) need not also be a ground for each logical consequence of \(A\).</li>
<li><em>Structure</em>: A ground for \(A\to B\) can be seen as a function from grounds for \(A\) to grounds for \(B\). A ground for \(A\land B\) can be seen as consisting of a ground for \(A\) and a ground for \(B\). A ground against \(A\lor B\) can be seen as consisting of a ground against \(A\) and a ground against \(B\). A ground for \(\neg A\) can be obtained from a ground against \(A\), and a ground against \(\neg A\) can be obtained from a ground for \(A\).</li>
</ol>
<p>The result is a model of grounds with significant similarities to the BHK interpretation of constructive logic, but for the classical sequent calculus.</p>
<ul>
<li><p>This is a talk for the <a href="http://blogs.unimelb.edu.au/logic/logic-seminar/">Melbourne Logic Seminar</a>.</p></li>
<li><p>The <a href="https://consequently.org/slides/new-work-for-a-theory-of-grounds-logicmelb.pdf">slides of the talk are available here</a>.</p></li>
</ul>
Truth and Stereotypes
https://consequently.org/presentation/2018/truth-and-stereotypes/
Sun, 21 Oct 2018 00:00:00 UTChttps://consequently.org/presentation/2018/truth-and-stereotypes/<p><em>Abstract</em>: Our thoughts and our conversations are filled with generalisations. From everyday trivialities such as <em>birds fly</em> or <em>trams are crowded</em> to contested claims such as <em>women are oppressed</em> or <em>Muslims are peace-loving</em>, we think and communicate using generalisations and stereotypes. This way of understanding the world is useful and pervasive, but at the same time, it has significant limitations.</p>
<p>In this lecture, I will explain some of the surprising features of these generalisations. Then I’ll apply some of the tools developed by philosophers of language over the last decades, in order to understand why generalisations and stereotypes are so pervasive; why they can behave so strangely and can sometimes lead us astray; and finally, to learn how we can use generalisations and stereotypes productively in our thinking and our communication.</p>
<ul>
<li>This is a <a href="https://events.unimelb.edu.au/events/11429-truth-and-stereotypes">free public lecture at the University of Melbourne</a>, held at 7pm in the Kathleen Fitzpatrick Lecture Theatre (Arts West). Although it’s free, it’s a good idea to <a href="http://alumni.online.unimelb.edu.au/GRestall">book tickets</a>.</li>
<li>The slides for the talk are <a href="https://consequently.org/slides/truth-and-stereotypes.pdf">available here</a>.</li>
</ul>
Philosophy in Public
https://consequently.org/news/2018/philosophy-in-public/
Sun, 28 Oct 2018 13:34:27 +1100https://consequently.org/news/2018/philosophy-in-public/<p>Last Wednesday, I went down to the studios at <a href="http://about.abc.net.au/press-releases/abc-opens-its-new-southbank-centre/">ABC Southbank</a>, to be interviewed by Libbi Gorr for ABC Radio Melbourne’s <a href="https://www.abc.net.au/radio/melbourne/programs/sundays/">Sunday program</a>. As I made my way through the building, and settled into the little studio, I thought I heard a familiar voice, faintly in the distance. Libbi explained that this was Kevin Rudd (the former Prime Minister), who was being interviewed in the next room. Unlike the former PM, I wasn’t doing the rounds of media because I had a book to promote. But I was doing promotion in my own small way. The <a href="http://newsroom.melbourne.edu/about">University of Melbourne’s Media Office</a> does a good job at getting the word out about public lectures, and the description for the lecture I’m giving on <a href="https://consequently.org/presentation/2018/truth-and-stereotypes/">Tuesday night</a> apparently appealed to Libbi Gorr and her producer, and they thought it would be fun to interview me for the Sunday program, so on Tuesday midday, I get an email from the Media Office asking if I’d be up for an interview in the studio with Libbi, talking about Truth and Stereotypes.</p>
<p>So, that’s why I found myself in the studio having a fun 20 minute conversation with Libbi about stereotypes, thoughts, language and communication, and the possibility of objectivity and agreement (or disagreement) when we’re all situated in different places and have different perspectives. It didn’t go in the directions I expected. But I wasn’t trying to stick to any particular talking points. The aim was to have a fruitful conversation, and to engage the audience with some interesting questions, and to spark interest in the topics I’ll be covering in my public lecture. The interview was edited down to 17 minutes, and <a href="https://www.abc.net.au/radio/melbourne/programs/sundays/greg-restall/10432666">the result is here</a>. If it gets people interested in thinking in a different way about things, and curious about what we do when we approach issues of language and meaning as philosophers, I’ll count that as a win.</p>
<p>So now, I’ve got to finish my preparation for <a href="https://consequently.org/presentation/2018/truth-and-stereotypes/">Tuesday’s lecture</a>.</p>
With help from Hugo, GitHub, Netlify, Working Copy and Shortcuts, I might update this website more frequently
https://consequently.org/news/2018/with-help-from-hugo-github-netlify-working-copy-and-shortcuts-i-might-update-this-website-more-frequently/
Sun, 21 Oct 2018 16:39:00 +1100https://consequently.org/news/2018/with-help-from-hugo-github-netlify-working-copy-and-shortcuts-i-might-update-this-website-more-frequently/<p>If you’ve been following my <a href="https://consequently.org/presentation/">travels</a>, you’ll get some sense that this has been a busy year. I’ve done lots of writing on my <a href="https://consequently.org/writing/ptrm">book</a>, and I’ve managed to give lots of talks, both in the US and in Argentina, as well as at home. I haven’t posted here for nearly a year–writing elsewhere has been a higher priority.</p>
<p>However, this weekend, I’ve made a few changes to the website which means that I might post here a little more often. The site is produced by <a href="http://gohugo.io">Hugo</a>, a really sweet static site generator. Until yesterday, if I wanted to update my site, what I did was</p>
<ol>
<li>Write files on whatever device I was using–most probably my Mac, but maybe my iPad–and push them to my my <a href="https://github.com/consequently/consequently-hugo">Git repository</a>, which contains the source for the whole website.</li>
<li>Then, on my Mac, sync up the repository.</li>
<li>Run hugo to update the generated files.</li>
<li>Sync the result up to GitHub.</li>
</ol>
<p>That worked fine, but I needed to do steps 2–4 on my Mac, and I don’t always have my Mac with me. Sometimes I prefer to write on my (smaller, less fiddly an distracting) iPad, and sometimes I only have my phone with me, and it’d be nice to update files on the website without having to run through my Mac to do that. I use <a href="http://workingcopyapp.com">Working Copy</a> on my iPhone and iPad to keep local copies of my website files (as well as the papers and book I’m currently working on) so it’s as easy as anything to edit these files wherever I have one of these devices on hand.</p>
<p>Here’s where <a href="http://netlify.com">Netlify</a> comes in. It’s a continuous integration service, that does step 2-4 in the cloud, without me having to be at my Mac. It’s <a href="https://gohugo.io/hosting-and-deployment/hosting-on-netlify/">very easy to wire up Netlify and Github</a> so that whenever I add a new file (or edit a file) in the source to my website, a little daemon spins up on the Netlify servers, runs hugo on the files, and syncs the result up to my website. It means that now I can edit files from any device connected to the internet, and the site is nicely generated, without me having to either edit in a web form (ugh!) or deal with a database driven website that either needs software maintenance or is prone to spam and server injection nastiness, or goes down at a drop of a hat. The site is still statically generated HTML, and I have control over how it is made. It’s a lovely solution.</p>
<p>So, over the weekend I’ve set things up, flipped the switches, and if you’re reading this, you’re reading the first entry written on my iPad and served up through the Netlify CI service.</p>
<p>The next step is to write some little <a href="https://support.apple.com/en-us/HT208309">Shortcuts</a> which make the job of creating new entries in the <a href="https://consequently.org/news/">News</a>, <a href="https://consequently.org/writing/">Writing</a>, <a href="https://consequently.org/class/">Class</a> and <a href="https://consequently.org/presentation/">Presentation</a> categories, with the datestamps and other boilerplate set automatically, even quicker, so there’s less friction in making new entries. I’ve done the first draft of the “News” shortcut already, and if you can see this entry, it means it’s worked.</p>
<p>As always, this is a work in progress, and probably things broke as I shifted things around. If you notice anything broken, please let me know. Thanks!</p>
Accommodation, Inference, Generics and Pejoratives
https://consequently.org/presentation/2018/accommodation-melb-workshop/
Wed, 10 Oct 2018 00:00:00 UTChttps://consequently.org/presentation/2018/accommodation-melb-workshop/<p><em>Abstract</em>: In this talk, I aim to give an account of norms governing our uses of <em>generic judgements</em> (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing <em>inference</em>, and the relationship <em>between</em> generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact that only female birds lay eggs?</p>
<p>Given the connection between generics and inference, I’ll go on to consider how inference relates to the process of <em>accommodation</em>, which plays a significant role in how we manage dialogue and conversation. This, in turn, helps shed some light on some different ways expressions can involve <em>pejorative force</em>, and can inform options for how our vocabulary and our concepts can be revised or reformed.</p>
<ul>
<li>This is a talk for a workshiop on Social Ontology at the University of Melbourne.</li>
<li>The <a href="https://consequently.org/slides/accommodation-melb-workshop.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/accommodation-melb-workshop-handout.pdf">handout is here</a>.</li>
</ul>
Accommodation, Inference, Generics and Pejoratives
https://consequently.org/presentation/2018/accommodation-uq/
Thu, 04 Oct 2018 00:00:00 UTChttps://consequently.org/presentation/2018/accommodation-uq/<p><em>Abstract</em>: In this talk, I aim to give an account of norms governing our uses of <em>generic judgements</em> (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing <em>inference</em>, and the relationship <em>between</em> generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact that only female birds lay eggs?</p>
<p>Given the connection between generics and inference, I’ll go on to consider how inference relates to the process of <em>accommodation</em>, which plays a significant role in how we manage dialogue and conversation. This, in turn, helps shed some light on some different ways expressions can involve <em>pejorative force</em>, and can inform options for how our vocabulary and our concepts can be revised or reformed.</p>
<ul>
<li>This is a <a href="https://hapi.uq.edu.au/event/session/3538">talk for the University of Queensland Philosophy Seminar Series</a> (3pm-5pm, Fridays).</li>
<li>The <a href="https://consequently.org/slides/accommodation-uq.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/accommodation-uq-handout.pdf">handout is here</a>.</li>
</ul>
Negation on the Australian Plan
https://consequently.org/writing/nap/
Tue, 18 Sep 2018 00:00:00 UTChttps://consequently.org/writing/nap/<p>We present and defend the Australian Plan semantics for negation. This is a comprehensive account, suitable for a variety of different logics. It is based on two ideas. The first is that negation is an exclusion-expressing device: we utter negations to express incompatibilities. The second is that, because incompat<em>ibility</em> is modal, negation is a modal operator as well. It can, then, be modelled as a quantifier over points in frames, restricted by accessibility relations representing compatibilities and incompatibilities between such points. We defuse a number of objections to this Plan, raised by supporters of the American Plan for negation, in which negation is handled via a many-valued semantics. We show that the Australian Plan has substantial advantages over the American Plan.</p>
Defining Rules, Proofs and Counterexamples
https://consequently.org/presentation/2018/defining-rules-proofs-and-counterexamples-ba-logic-vii/
Thu, 26 Jul 2018 00:00:00 UTChttps://consequently.org/presentation/2018/defining-rules-proofs-and-counterexamples-ba-logic-vii/<p><em>Abstract</em>: In this talk, I will present an account of <em>defining rules</em>, with the aim of explaining these rules they play a central role in analytic proofs. Along the way, I’ll explain how Kreisel’s <em>squeezing argument</em> helps us understand the connection between an informal notion of validity and the notions formalised in our accounts of proofs and models, and the relationship between proof-theoretic and model- theoretic analyses of logical consequence.</p>
<ul>
<li><p>This is a talk for the <a href="http://ba-logic.com/workshops/7th-workshop/">VII Workshop on Philosophical Logic</a>.</p></li>
<li><p>The <a href="https://consequently.org/slides/defining-rules-proofs-and-counterexamples-slides.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/defining-rules-proofs-and-counterexamples-handout.pdf">handout is here</a>.</p></li>
</ul>
Proof Theory, Rules and Meaning — an introduction
https://consequently.org/presentation/2018/proof-theory-rules-and-meaning/
Mon, 30 Jul 2018 00:00:00 UTChttps://consequently.org/presentation/2018/proof-theory-rules-and-meaning/<p><em>Abstract</em>: I introduce the key themes from my book-in-progress, <a href="https://consequently.org/writing/ptrm/">Proof Theory, Rules and Meaning</a>.</p>
<ul>
<li><p>This is a talk for the <a href="http://ba-logic.com/workshops/symposium-restall/">symposium</a> on the manuscript held at the Argentinean Society of Philosophical Analysis (SADAF) in Buenos Aires, in July 2018.</p></li>
<li><p>The <a href="https://consequently.org/slides/proof-theory-rules-and-meaning-intro-ba.pdf">slides for the talk are available here</a>.</p></li>
</ul>
PHIL30043: The Power and Limits of Logic
https://consequently.org/class/2018/phil30043/
Mon, 16 Jul 2018 00:00:00 UTChttps://consequently.org/class/2018/phil30043/
<p><strong><span class="caps">PHIL30043</span>: The Power and Limits of Logic</strong> is a <a href="https://handbook.unimelb.edu.au/view/2018/PHIL30043">University of Melbourne undergraduate subject</a>. It covers the metatheory of classical first order predicate logic, beginning at the <em>Soundness</em> and <em>Completeness</em> Theorems (proved not once but <em>twice</em>, first for a tableaux proof system for predicate logic, then a Hilbert proof system), through the <em>Deduction Theorem</em>, <em>Compactness</em>, <em>Cantor’s Theorem</em>, the <em>Downward Löwenheim–Skolem Theorem</em>, <em>Recursive Functions</em>, <em>Register Machines</em>, <em>Representability</em> and ending up at <em>Gödel’s Incompleteness Theorems</em> and <em>Löb’s Theorem</em>.</p>
<figure>
<img src="https://consequently.org/images/godel.jpg" alt="Kurt Godel, seated">
<figcaption>Kurt Gödel, seated</figcaption>
</figure>
<p>The subject is taught to University of Melbourne undergraduate students (for Arts students as a part of the Philosophy major, for non-Arts students, as a breadth subject). Details for enrolment are <a href="https://handbook.unimelb.edu.au/view/2018/PHIL30043">here</a>. I make use of video lectures I have made <a href="http://vimeo.com/album/2262409">freely available on Vimeo</a>.</p>
<h3 id="outline">Outline</h3>
<p>The course is divided into four major sections and a short prelude. Here is a list of all of the videos, in case you’d like to follow along with the content.</p>
<h4 id="prelude">Prelude</h4>
<ul>
<li><a href="http://vimeo.com/album/2262409/video/59401942">Logical Equivalence</a></li>
<li><a href="http://vimeo.com/album/2262409/video/59403292">Disjunctive Normal Form</a></li>
<li><a href="http://vimeo.com/album/2262409/video/59403535">Why DNF Works</a></li>
<li><a href="http://vimeo.com/album/2262409/video/59463569">Prenex Normal Form</a></li>
<li><a href="http://vimeo.com/album/2262409/video/59466141">Models for Predicate Logic</a></li>
<li><a href="http://vimeo.com/album/2262409/video/59880539">Trees for Predicate Logic</a></li>
</ul>
<h4 id="completeness">Completeness</h4>
<ul>
<li><a href="http://vimeo.com/album/2262409/video/59883806">Introducing Soundness and Completeness</a></li>
<li><a href="http://vimeo.com/album/2262409/video/60249309">Soundness for Tree Proofs</a></li>
<li><a href="http://vimeo.com/album/2262409/video/60250515">Completeness for Tree Proofs</a></li>
<li><a href="http://vimeo.com/album/2262409/video/61677028">Hilbert Proofs for Propositional Logic</a></li>
<li><a href="http://vimeo.com/album/2262409/video/61685762">Conditional Proof</a></li>
<li><a href="http://vimeo.com/album/2262409/video/62221512">Hilbert Proofs for Predicate Logic</a></li>
<li><a href="http://vimeo.com/album/2262409/video/103720089">Theories</a></li>
<li><a href="http://vimeo.com/album/2262409/video/103757399">Soundness and Completeness for Hilbert Proofs for Predicate Logic</a></li>
</ul>
<h4 id="compactness">Compactness</h4>
<ul>
<li><a href="http://vimeo.com/album/2262409/video/63454250">Counting Sets</a></li>
<li><a href="http://vimeo.com/album/2262409/video/63454732">Diagonalisation</a></li>
<li><a href="http://vimeo.com/album/2262409/video/63454732">Compactness</a></li>
<li><a href="http://vimeo.com/album/2262409/video/63455121">Non-Standard Models</a></li>
<li><a href="http://vimeo.com/album/2262409/video/63462354">Inexpressibility of Finitude</a></li>
<li><a href="http://vimeo.com/album/2262409/video/63462519">Downward Löwenheim–Skolem Theorem</a></li>
</ul>
<h4 id="computability">Computability</h4>
<ul>
<li><a href="http://vimeo.com/album/2262409/video/64162062">Functions</a></li>
<li><a href="http://vimeo.com/album/2262409/video/64167354">Register Machines</a></li>
<li><a href="http://vimeo.com/album/2262409/video/64207986">Recursive Functions</a></li>
<li><a href="http://vimeo.com/album/2262409/video/64435763">Register Machine computable functions are Recursive</a></li>
<li><a href="http://vimeo.com/album/2262409/video/64604717">The Uncomputable</a></li>
</ul>
<h4 id="undecidability-and-incompleteness">Undecidability and Incompleteness</h4>
<ul>
<li><a href="http://vimeo.com/album/2262409/video/65382456">Deductively Defined Theories</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65392670">The Finite Model Property</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65393543">Completeness</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65440901">Introducing Robinson’s Arithmetic</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65442289">Induction and Peano Arithmetic</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65443650">Representing Functions and Sets</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65483655">Gödel Numbering and Diagonalisation</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65497886">Q (and any consistent extension of Q) is undecidable, and incomplete if it’s deductively defined</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65498016">First Order Predicate Logic is Undecidable</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65501745">True Arithmetic is not Deductively Defined</a></li>
<li><a href="http://vimeo.com/album/2262409/video/65505372">If Con(PA) then PA doesn’t prove Con(PA)</a></li>
</ul>
PHIL20030: Meaning, Possibility and Paradox
https://consequently.org/class/2018/phil20030/
Mon, 16 Jul 2018 00:00:00 UTChttps://consequently.org/class/2018/phil20030/
<p><strong><span class="caps">PHIL20030</span>: Meaning, Possibility and Paradox</strong> is a <a href="http://unimelb.edu.au">University of Melbourne</a> undergraduate subject. The idea that the meaning of a sentence depends on the meanings of its parts is fundamental to the way we understand logic, language and the mind. In this subject, we look at the different ways that this idea has been applied in logic throughout the 20th Century and into the present day.</p>
<p>In the first part of the subject, our focus is on the concepts of necessity and possibility, and the way that ‘possible worlds semantics’ has been used in theories of meaning. We will focus on the logic of necessity and possibility (modal logic), times (temporal logic), conditionality and dependence (counterfactuals), and the notions of analyticity and a priority so important to much of philosophy.</p>
<p>In the second part of the subject, we examine closely the assumption that every statement we make is either true or false but not both. We will examine the paradoxes of truth (like the so-called ‘liar paradox’) and vagueness (the ‘sorites paradox’), and we will investigate different ways attempts at resolving these paradoxes by going beyond our traditional views of truth (using ‘many valued logics’) or by defending the traditional perspective.</p>
<p>The subject serves as an introduction to ways that logic is applied in the study of language, epistemology and metaphysics, so it is useful to those who already know some philosophy and would like to see how logic relates to those issues. It is also useful to those who already know some logic and would like to learn new logical techniques and see how these techniques can be applied.</p>
<p>The subject is offered to University of Melbourne undergraduate students (for Arts students as a part of the Philosophy major, for non-Arts students, as a breadth subject). Details for enrolment are <a href="https://handbook.unimelb.edu.au/view/2018/PHIL20030">here</a>.</p>
<figure>
<img src="https://consequently.org/images/peter-rozsa-small.png" alt="Rosza Peter">
<figcaption>The writing down of a formula is an expression of our joy that we can answer all these questions by means of one argument. — Rózsa Péter, Playing with Infinity</figcaption>
</figure>
<p>I make use of video lectures I have made <a href="http://vimeo.com/album/2470375">freely available on Vimeo</a>. If you’re interested in this sort of thing, I hope they’re useful. Of course, I appreciate any constructive feedback you might have.</p>
<h3 id="outline">Outline</h3>
<p>The course is divided into four major sections and a short prelude. Here is a list of all of the videos, in case you’d like to follow along with the content.</p>
<h4 id="classical-logic">Classical Logic</h4>
<ul>
<li><a href="https://vimeo.com/album/2470375/video/71195118">On Logic and Philosophy</a></li>
<li><a href="https://vimeo.com/album/2470375/video/71196826">Classical Logic—Models</a></li>
<li><a href="https://vimeo.com/album/2470375/video/71200032">Classical Logic—Tree Proofs</a></li>
</ul>
<h4 id="meaning-sense-reference">Meaning, Sense, Reference</h4>
<ul>
<li><a href="https://vimeo.com/album/2470375/video/71206884">Reference and Compositionality</a></li>
<li><a href="https://vimeo.com/album/2470375/video/71226471">Sense and Reference</a></li>
</ul>
<h4 id="basic-modal-logic">Basic Modal Logic</h4>
<ul>
<li><a href="https://vimeo.com/album/2470375/video/71556216">Introducing Possibility an Necessity</a></li>
<li><a href="https://vimeo.com/album/2470375/video/71558401">Models for Basic Modal Logic</a></li>
<li><a href="https://vimeo.com/album/2470375/video/71558696">Tree Proofs for Basic Modal Logic</a></li>
<li><a href="https://vimeo.com/album/2470375/video/71560394">Soundness and Completeness for Basic Modal Logic</a></li>
</ul>
<h4 id="normal-modal-logics">Normal Modal Logics</h4>
<ul>
<li><a href="https://vimeo.com/album/2470375/video/72135540">What Are Possible Worlds?</a></li>
<li><a href="https://vimeo.com/album/2470375/video/72137443">Conditions on Accessibility Relations</a></li>
<li><a href="https://vimeo.com/album/2470375/video/72137856">Equivalence Relations, Universal Relations and S5</a></li>
<li><a href="https://vimeo.com/album/2470375/video/72139085">Tree Proofs for Normal Modal Logic</a></li>
<li><a href="https://vimeo.com/album/2470375/video/72140275">Applying Modal Logics</a></li>
</ul>
<h4 id="double-indexing">Double Indexing</h4>
<ul>
<li><a href="https://vimeo.com/album/2470375/video/72140275">Temporal Logic</a></li>
<li><a href="https://vimeo.com/album/2470375/video/72143616">Actuality and the Present</a></li>
<li><a href="https://vimeo.com/album/2470375/video/72266887">Two Dimensional Modal Logic</a></li>
</ul>
<h4 id="conditionality">Conditionality</h4>
<ul>
<li><a href="https://vimeo.com/album/2470375/video/74494229">Strict Conditionals</a></li>
<li><a href="https://vimeo.com/album/2470375/video/74498276"><em>Ceteris Paribus</em> Conditionals</a></li>
<li><a href="https://vimeo.com/album/2470375/video/74504639">Similarity</a></li>
</ul>
<h4 id="three-values">Three Values</h4>
<ul>
<li><a href="https://vimeo.com/album/2470375/video/74628150">More than Two Truth Values</a></li>
<li><a href="https://vimeo.com/album/2470375/video/74636384">K3</a></li>
<li><a href="https://vimeo.com/album/2470375/video/74680756">Ł3</a></li>
<li><a href="https://vimeo.com/album/2470375/video/74680954">LP</a></li>
<li><a href="https://vimeo.com/album/2470375/video/74682689">RM3</a></li>
</ul>
<h4 id="four-values">Four Values</h4>
<ul>
<li><a href="https://vimeo.com/album/2470375/video/74685077">FDE: Relational Evaluations</a></li>
<li><a href="https://vimeo.com/album/2470375/video/74685986">FDE: Tree Proofs</a></li>
<li><a href="https://vimeo.com/album/2470375/video/74695340">FDE: Routley Evaluations</a></li>
</ul>
<h4 id="paradoxes">Paradoxes</h4>
<ul>
<li><a href="https://vimeo.com/album/2470375/video/76045884">Truth and the Liar Paradox</a></li>
<li><a href="https://vimeo.com/album/2470375/video/76049193">Fixed Point Construction</a></li>
<li><a href="https://vimeo.com/album/2470375/video/76055233">Curry’s Paradox</a></li>
<li><a href="https://vimeo.com/album/2470375/video/76057722">The Sorites Paradox</a></li>
<li><a href="https://vimeo.com/album/2470375/video/76061452">Fuzzy Logic</a></li>
<li><a href="https://vimeo.com/album/2470375/video/76066245">Supervaluationism</a></li>
<li><a href="https://vimeo.com/album/2470375/video/76070423">Epistemicism</a></li>
</ul>
<h4 id="what-to-do-with-so-many-logical-systems">What to do with so many logical systems</h4>
<ul>
<li><a href="https://vimeo.com/album/2470375/video/76070953">Logical Monism and Pluralism</a></li>
</ul>
What Proofs are For
https://consequently.org/presentation/2018/what-proofs-are-for-melbourne-glasgow/
Thu, 07 Jun 2018 00:00:00 UTChttps://consequently.org/presentation/2018/what-proofs-are-for-melbourne-glasgow/<p><em>Abstract</em>: In this short talk, I present a new account of the nature of proof, with the aim of explaining how proof could actually play the role in reasoning that it does, and answering some long-standing puzzles about the nature of proof. Along the way, I’ll explain how Kreisel’s Squeezing argument helps us understand the connection between an informal notion of of validity and the notions formalised in our accounts of proofs and models, and the relationship between proof-theoretic and model-theoretic analyses of logical consequence.</p>
<ul>
<li><p>This is a talk for the <a href="https://philevents.org/event/show/41790">Melbourne–Glasgow Formal Philosophy Workshop</a>.</p></li>
<li><p>The <a href="https://consequently.org/slides/what-proofs-are-for-melbourne-glasgow-slides.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/what-proofs-are-for-melbourne-glasgow-handout.pdf">handout is here</a>.</p></li>
</ul>
Isomorphisms in a Category of Proofs
https://consequently.org/presentation/2018/mit-sllerg/
Fri, 05 Jan 2018 00:00:00 UTChttps://consequently.org/presentation/2018/mit-sllerg/<p><em>Abstract</em>: In this talk, I show how a category of formulas and classical proofs can give rise to three different hyperintensional notions of sameness of content. One of these notions is very fine-grained, going so far as to distinguish \(p\) and \(p\land p\), while identifying other distinct pairs of formulas, such as \(p\land q\) and \(q\land p\); \(p\) and \(\neg\neg p\); or \(\neg(p\land q)\) and \(\neg p\lor\neg q\). Another relation is more coarsely grained, and gives the same account of identity of content as equivalence in Angell’s logic of analytic containment. A third notion of sameness of content is defined, which is intermediate between Angell’s and Parry’s logics of analytic containment. Along the way we show how purely classical proof theory gives resources to define hyperintensional distinctions thought to be the domain of properly non-classical logics.</p>
<ul>
<li>This is a talk for the MIT SLLERG Group.</li>
<li>The <a href="https://consequently.org/slides/isomorphisms-talk-mit-2018.pdf">slides can be downloaded here</a>, but the <a href="https://consequently.org/handouts/isomorphisms-handout-mit-2018.pdf">handout</a> (4 pages) is best for printing out and reading, so it’s probably better that you <a href="https://consequently.org/handouts/isomorphisms-handout-mit-2018.pdf">download and print that</a>.</li>
</ul>
Accommodation, Inference, Generics and Pejoratives
https://consequently.org/presentation/2018/mit-wip/
Fri, 05 Jan 2018 00:00:00 UTChttps://consequently.org/presentation/2018/mit-wip/<p><em>Abstract</em>: In this talk, I aim to give an account of norms governing our uses of <em>generic judgements</em> (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing <em>inference</em>, and the relationship <em>between</em> generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact that only female birds lay eggs?</p>
<p>Given the connection between generics and inference, I’ll go on to consider how inference relates to the process of <em>accommodation</em>, which plays a significant role in how we manage dialogue and conversation. This, in turn, helps shed some light on some different ways expressions can involve <em>pejorative force</em>, and can inform options for how our vocabulary and our concepts can be revised or reformed.</p>
<ul>
<li>This is a talk for the MIT Philosophy Work in Progress series (1pm-2pm, Thursdays).</li>
<li>The <a href="https://consequently.org/slides/accommodation-mit.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/accommodation-mit-handout.pdf">handout is here</a>.</li>
</ul>
Accommodation, Inference, Generics and Pejoratives
https://consequently.org/presentation/2018/uconn-brown-bag/
Fri, 05 Jan 2018 00:00:00 UTChttps://consequently.org/presentation/2018/uconn-brown-bag/<p><em>Abstract</em>: In this talk, I aim to give an account of norms governing our uses of <em>generic judgements</em> (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing <em>inference</em>, and the relationship <em>between</em> generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact that only female birds lay eggs?</p>
<p>Given the connection between generics and inference, I’ll go on to consider how inference relates to the process of <em>accommodation</em>, which plays a significant role in how we manage dialogue and conversation. This, in turn, helps shed some light on some different ways expressions can involve <em>pejorative force</em>, and can inform options for how our vocabulary and our concepts can be revised or reformed.</p>
<ul>
<li>This is a talk for the <a href="http://events.uconn.edu/event/60881/2018-04-18">University of Connecticut Philosophy Brown Bag</a>.</li>
<li>The <a href="https://consequently.org/slides/accommodation-uconn.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/accommodation-uconn-handout.pdf">handout is here</a>.</li>
</ul>
Accommodation, Inference, Generics and Pejoratives
https://consequently.org/presentation/2018/pitt-philosophy-colloquium/
Fri, 05 Jan 2018 00:00:00 UTChttps://consequently.org/presentation/2018/pitt-philosophy-colloquium/<p><em>Abstract</em>: In this talk, I aim to give an account of norms governing our uses of <em>generic judgements</em> (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing <em>inference</em>, and the relationship <em>between</em> generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact that only female birds lay eggs?</p>
<p>Given the connection between generics and inference, I’ll go on to consider how inference relates to the process of <em>accommodation</em>, which plays a significant role in how we manage dialogue and conversation. This, in turn, helps shed some light on some different ways expressions can involve <em>pejorative force</em>, and can inform options for how our vocabulary and our concepts can be revised or reformed.</p>
<ul>
<li>This is a talk for the <a href="http://www.philosophy.pitt.edu/event/greg-restall-u-melbourne-talk">University of Pittsburgh Philosophy Colloquium</a>.</li>
<li>The <a href="https://consequently.org/slides/accommodation-pitt.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/accommodation-pitt-handout.pdf">handout is here</a>.</li>
</ul>
Isomorphisms in a Category of Proofs
https://consequently.org/presentation/2018/cmu-pure-and-applied-logic/
Fri, 05 Jan 2018 00:00:00 UTChttps://consequently.org/presentation/2018/cmu-pure-and-applied-logic/<p><em>Abstract</em>: In this talk, I show how a category of formulas and classical proofs can give rise to three different hyperintensional notions of sameness of content. One of these notions is very fine-grained, going so far as to distinguish \(p\) and \(p\land p\), while identifying other distinct pairs of formulas, such as \(p\land q\) and \(q\land p\); \(p\) and \(\neg\neg p\); or \(\neg(p\land q)\) and \(\neg p\lor\neg q\). Another relation is more coarsely grained, and gives the same account of identity of content as equivalence in Angell’s logic of analytic containment. A third notion of sameness of content is defined, which is intermediate between Angell’s and Parry’s logics of analytic containment. Along the way we show how purely classical proof theory gives resources to define hyperintensional distinctions thought to be the domain of properly non-classical logics.</p>
<ul>
<li>This is a <a href="https://calendar.google.com/calendar/event?eid=NG4zNDZkbXA5OTRqNzEwcDVpdTZhcHZjbm8gMDFsMXQ2c2I1dGJhcWk2NmJnOGIxOWszN29AZw&ctz=America/New_York">talk for the CMU Pure and Applied Logic Seminar Series</a>.</li>
<li>The <a href="https://consequently.org/slides/isomorphisms-talk-cmu-2018.pdf">slides can be downloaded here</a>, but the <a href="https://consequently.org/handouts/isomorphisms-handout-cmu-2018.pdf">handout</a> (4 pages) is best for printing out and reading, so it’s probably better that you <a href="https://consequently.org/handouts/isomorphisms-handout-cmu-2018.pdf">download and print that</a>.</li>
</ul>
Isomorphisms in a Category of Proofs
https://consequently.org/presentation/2018/cuny-gc-logic-and-metaphysics/
Fri, 05 Jan 2018 00:00:00 UTChttps://consequently.org/presentation/2018/cuny-gc-logic-and-metaphysics/<p><em>Abstract</em>: In this talk, I show how a category of classical proofs can give rise to three different hyperintensional notions of sameness of content. One of these notions is very fine-grained, going so far as to distinguish \(p\) and \(p\land p\), while identifying other distinct pairs of formulas, such as \(p\land q\) and \(q\land p\); \(p\) and \(\neg\neg p\); or \(\neg(p\land q)\) and \(\neg p\lor\neg q\). Another relation is more coarsely grained, and gives the same account of identity of content as equivalence in Angell’s logic of analytic containment. A third notion of sameness of content is defined, which is intermediate between Angell’s and Parry’s logics of analytic containment. Along the way we show how purely classical proof theory gives resources to define hyperintensional distinctions thought to be the domain of properly non-classical logics.</p>
<ul>
<li><p>This is a talk for the <a href="https://logic.commons.gc.cuny.edu">CUNY Graduate Center Logic and Metaphysics Seminar</a>.</p></li>
<li><p>The <a href="https://consequently.org/slides/isomorphisms-talk-cuny-2018.pdf">slides can be downloaded here</a>, but the <a href="https://consequently.org/handouts/isomorphisms-handout-cuny-2018.pdf">handout</a> (4 pages) is best for printing out and reading, so it’s probably better that you <a href="https://consequently.org/handouts/isomorphisms-handout-cuny-2018.pdf">download and print that</a>.</p></li>
</ul>
What Proofs are For
https://consequently.org/presentation/2018/what-proofs-are-for-nyu/
Fri, 05 Jan 2018 00:00:00 UTChttps://consequently.org/presentation/2018/what-proofs-are-for-nyu/<p><em>Abstract</em>: In this short talk, I present a new account of the nature of proof, with the aim of explaining how proof could actually play the role in reasoning that it does, and answering some long-standing puzzles about the nature of proof. Along the way, I’ll explain how Kreisel’s Squeezing argument helps us understand the connection between an informal notion of of validity and the notions formalised in our accounts of proofs and models, and the relationship between proof-theoretic and model-theoretic analyses of logical consequence.</p>
<ul>
<li><p>This is a talk for the NYU Philosophy Department Brown Bag Series.</p></li>
<li><p>The <a href="https://consequently.org/slides/what-proofs-are-for-nyu-slides.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/what-proofs-are-for-nyu-handout.pdf">handout is here</a>.</p></li>
</ul>
Accommodation, Inference, Generics and Pejoratives
https://consequently.org/presentation/2018/cuny-gc-colloquium/
Fri, 05 Jan 2018 00:00:00 UTChttps://consequently.org/presentation/2018/cuny-gc-colloquium/<p><em>Abstract</em>: In this talk, I aim to give an account of norms governing our uses of <em>generic judgements</em> (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing <em>inference</em>, and the relationship <em>between</em> generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact that only female birds lay eggs?</p>
<p>Given the connection between generics and inference, I’ll go on to consider how inference relates to the process of <em>accommodation</em>, which plays a significant role in how we manage dialogue and conversation. This, in turn, helps shed some light on some different ways expressions can involve <em>pejorative force</em>, and can inform options for how our vocabulary and our concepts can be revised or reformed.</p>
<ul>
<li><p>This is a talk for the <a href="https://philosophy.commons.gc.cuny.edu/spring-2018-colloquium-schedule/">CUNY Graduate Center Philosophy Colloquium</a>.</p></li>
<li><p>The <a href="https://consequently.org/slides/accommodation-cuny-2018.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/accommodation-cuny-handout-2018.pdf">handout is here</a>.</p></li>
</ul>
Accommodation, Inference, Generics and Pejoratives
https://consequently.org/presentation/2018/unimelb-accommodation/
Tue, 13 Feb 2018 00:00:00 UTChttps://consequently.org/presentation/2018/unimelb-accommodation/<p><em>Abstract</em>: In this talk, I aim to give an account of norms governing our uses of <em>generic judgements</em> (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing <em>inference</em>, and the relationship <em>between</em> generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact that only female birds lay eggs?</p>
<p>Given the connection between generics and inference, I’ll go on to consider how inference relates to the process of <em>accommodation</em>, which plays a significant role in how we manage dialogue and conversation. This, in turn, helps shed some light on some different ways expressions can involve <em>pejorative force</em>, and can inform options for how our vocabulary and our concepts can be revised or reformed.</p>
<ul>
<li><p>This is a talk for the <em><a href="https://philevents.org/event/show/42298">University of Melbourne Thursday Philosophy Seminar</a></em>.</p></li>
<li><p>The <a href="https://consequently.org/slides/accommodation-unimelb-2018.pdf">slides for the talk are available here</a>, and the <a href="https://consequently.org/handouts/accommodation-unimelb-handout-2018.pdf">handout is here</a>.</p></li>
</ul>
Truth Tellers in Bradwardine's Theory of Truth
https://consequently.org/writing/bradwardine-truth-tellers/
Wed, 21 Mar 2018 00:00:00 UTChttps://consequently.org/writing/bradwardine-truth-tellers/<p>Stephen Read’s work on Bradwardine’s theory of truth is some of the most exciting work on truth and insolubilia in recent years. Read brings together modern tools of formal logic and Bradwardine’s theory of signification to show that medieval distinctions can give great insight into the behaviour of semantic concepts such as truth. In a number of papers, I have developed a model theory for Bradwardine’s account of truth. This model theory has distinctive features: it serves up models in which every declarative object (any object signifying <em>anything</em>) signifies its own truth. This leads to a puzzle: there are good arguments to the effect that if anything is a truth-teller, it is <em>false</em>. This is a puzzle. What distinguishes <em>paradoxical</em> truth-tellers from <em>benign</em> truth tellers? It is my task in this paper to explain this distinction, and to clarify the behaviour of truth-tellers, given Bradwardine’s account of signification.</p>
Isomorphisms in a Category of Propositions and Proofs
https://consequently.org/presentation/2018/logicmelb-isomorphisms/
Tue, 13 Feb 2018 00:00:00 UTChttps://consequently.org/presentation/2018/logicmelb-isomorphisms/<p><em>Abstract</em>: In this talk, I show how a category of propositions and classical proofs can give rise to three different hyperintensional notions of sameness of content. One of these notions is very fine-grained, going so far as to distinguish \(p\) and \(p\land p\), while identifying other distinct pairs of formulas, such as \(p\land q\) and \(q\land p\); \(p\) and \(\neg\neg p\); or \(\neg(p\land q)\) and \(\neg p\lor\neg q\). Another relation is more coarsely grained, and gives the same account of identity of content as equivalence in Angell’s logic of analytic containment. A third notion of sameness of content is defined, which is intermediate between Angell’s and Parry’s logics of analytic containment. Along the way we show how purely classical proof theory gives resources to define hyperintensional distinctions thought to be the domain of properly non-classical logics.</p>
<ul>
<li><p>This is a talk for the <a href="blogs.unimelb.edu.au/logic/logic-seminar/">Melbourne Logic Seminar</a>.</p></li>
<li><p>The <a href="https://consequently.org/slides/isomorphisms-talk-unimelb-2018.pdf">slides of the talk are available here</a>, and the <a href="https://consequently.org/handouts/isomorphisms-handout-unimelb-2018.pdf">handout is here</a>.</p></li>
</ul>
Substructural Logics
https://consequently.org/writing/slintro/
Wed, 21 Feb 2018 00:00:00 UTChttps://consequently.org/writing/slintro/<p><i>Substructural logics</i> are non-classical logics <i>weaker</i> than classical logic, notable for the absence of <i>structural rules</i> present in classical logic. These logics are motivated by considerations from philosophy (relevant logics), linguistics (the Lambek calculus) and computing (linear logic). In addition, techniques from substructural logics are useful in the study of traditional logics such as classical and intuitionistic logic. This article provides an overview of the field of substructural logic.</p>
Community (the twelfth of twelve things I love about philosophical logic)
https://consequently.org/news/2017/twelve-things-12-community/
Sat, 30 Dec 2017 17:12:57 +1100https://consequently.org/news/2017/twelve-things-12-community/<p>I love the way I’ve met so many different people through working in logic, that I’ve made good friends, good colleagues, good teachers and mentors. I’ve been part of an enterprise that’s larger than any one person. I have been shaped by that community, and have had the opportunity to made some small mark on it myself.</p>
<p>Logic, like any other academic discipline, has a history. The activities of <em>doing</em> logic — of <em>studying</em>, <em>researching</em> and <em>teaching</em> — are spread out through time. Those activities are also, equally, spread out in space. Logic is done in many different places, in many different contexts, by many different individuals, and research teams. As I’ve already pointed out, those activities are shaped by different disciplinary connections (into philosophy, mathematics, computer science, linguistics, engineering, etc.), but they are also shaped by the emphases of different research groups and traditions. Research, these days, is dominated not so much by a small number of iconic logicians, but by research groups with distinctive research programmes.</p>
<p>Here are some examples: think of the difference between Amsterdam-style modal logic, on the one hand, and exact truthmaking semantics on the other, concerning approaches to intensionality and hyperintensionality, or for examples on the proof theoretical side of the street, the different traditions of Higher Order Type Theory and of Linear Logic and Ludics as frameworks for understanding proof, computation and meaning. The differences between these traditions are not simply matters of differences between individual researchers and their emphases — though of course, there are significant founding figures for each tradition I mention — the driving forces in each of these active research programmes is at the level of the <em>team</em> or beyond. Each approach brings with it a (larger or smaller) loose formation of researchers who work on problems in their fields: they get together at conferences and workshops, co-author papers, apply for research grants, supervise graduate students, all the while, maintaining and developing the tradition. Research that leaves a mark is not so much the activity of the brilliant sole researcher, it occurs at a larger scale.</p>
<p>Recognising this fact brings important questions to the fore: given that research at this scale is a community enterprise, how does that community function? Who is included? Who is excluded? How are people trained and shaped? What kinds of conversations are possible? What approaches are encouraged? My little corner of philosophical logic is only beginning to explicitly address some of these issues. <a href="https://gillianrussell.net">Gill Russell</a> and worked to get a decent gender balance in our <a href="http://consequently.org/writing/new-waves-in-philosophical-logic/">edited collection</a>. We partly succeeded on that front. We fail, mightily, on including participants from outside Europe, America and Australia. Further, the group of authors is overwhelmingly white. We could have done better. There is scope for the community to be more representative of thew wider community around us. Lasting change will require more than just good will and effort from individuals: it will involve broader social change, so that the oppressed and excluded get their due, and all to have the opportunities currently afforded to those who have the easiest access to higher education. That social change won’t come easy. However, those of us with the institutional capital to be able to shape and support research groups nonetheless have the opportunity to leave the discipline better than we found it, with a wider spectrum of voices included, with all people treated well, and a broader family of concerns taken seriously. We can run conferences where people are treated well; we can mentor and support our students, both women and men; we can encourage the work of those whose voices are routinely excluded, and so, build up a community that is resilient and flourishing.</p>
<p>As for me, I’ve been fortunate, more fortunate than I can readily discern. Not only have I been shaped by encouraging and supportive teachers and mentors throughout my own research career, but unlike many of my female colleagues, I’ve not been harassed or endangered. No-one has attempted to take advantage of me, or pass my work off as theirs. Overwhelmingly, people in my field have taken me seriously, even when I was a blundering student, attempting to find my way in the wider academic world. The reception I’ve had in the wider academic world is the kind of community I want for those coming after me.</p>
<p><em>Community</em> is the twelfth of <a href="http://consequently.org/news/2017/twelve-things-i-love/">twelve things that I love about philosophical logic</a>.</p>
Proof Identity, Aboutness and Meaning
https://consequently.org/presentation/2017/proof-identity-aboutness-and-meaning/
Mon, 06 Nov 2017 00:00:00 UTChttps://consequently.org/presentation/2017/proof-identity-aboutness-and-meaning/<p><em>Abstract</em>: This talk is a comparison of how different approaches to hyperintensionality, aboutness and subject matter treat (classically) logically equivalent statements. I compare and contrast two different notions of subject matter that might be thought to be representational or truth first – <em><a href="https://www.amazon.com/Aboutness-Carl-G-Hempel-Lecture/dp/0691144958/consequentlyorg">Aboutness</a></em> (Princeton University Press, 2014), and truthmakers conceived of as situations, as discussed in my “<a href="http://consequently.org/writing/ten/">Truthmakers, Entailment and Necessity</a>.” I contrast this with the kind of inferentialist account of hyperintensionality arising out of the <em>proof invariants</em> I have explored <a href="http://consequently.org/writing/proof-terms-for-classical-derivations/">in recent work</a>.</p>
<p>This is a talk presented at the <a href="https://www.gla.ac.uk/schools/humanities/research/philosophyresearch/researchprojects/thewholetruth/formalphilosophy/">Glasgow-Melbourne Formal Philosophy Workshop</a>.</p>
<ul>
<li>The <a href="http://consequently.org/slides/proof-identity-aboutness-and-meaning.pdf">slides are available here</a>.</li>
</ul>
Negation on the Australian Plan
https://consequently.org/presentation/2017/negation-on-the-australian-plan/
Wed, 23 Aug 2017 00:00:00 UTChttps://consequently.org/presentation/2017/negation-on-the-australian-plan/<p><em>Abstract</em>: In this talk, I explain the difference between <em>Australian Plan</em> semantics for negation – which treat negation as a kind of negative modality – and semantics based on the <em>American Plan</em>, which conceive of negation in terms of independent truth and falsity conditions. I will update the presentation of the Australian Plan (introduced in the 1970s in early days of the ternary relational semantics for relevant logics), in the light of more recent developments in logic, and defend this updated plan in the face of some recent criticisms due to <a href="http://www.michaelde.com">Michael De</a> and <a href="https://sites.google.com/site/hitoshiomori/home">Hitoshi Omori</a>, in their paper “<a href="http://dx.doi.org/10.1007/s10992-017-9427-0">There is More to Negation than Modality</a>.” Along the way, I hope to draw out some insights into what we might want out of a representational semantics for a language with a consequence relation.</p>
<p>This talk is based on joint work with <a href="http://www.uva.nl/en/profile/b/e/f.berto/f.berto.html">Professor Franz Berto</a>, from the University of Amsterdam.</p>
<p>This is a talk presented at the <a href="http://blogs.unimelb.edu.au/logic/logic-seminar/">Melbourne Logic Seminar</a>.</p>
<ul>
<li>The <a href="https://consequently.org/slides/negation-on-the-australian-plan-logicmelb.pdf">slides are available here</a>.</li>
</ul>
Learning and Teaching (the eleventh of twelve things I love about philosophical logic)
https://consequently.org/news/2017/twelve-things-11-learning-and-teaching/
Tue, 19 Sep 2017 22:47:48 +1100https://consequently.org/news/2017/twelve-things-11-learning-and-teaching/<p>Working in philosophical logic, I love the opportunity to <em>learn</em> from so many people through history, and not only to <em>learn</em>, but to pass on a tradition, and to have the opportunity to extend the tradition, and to refine it a little, in passing it on. It’s been a delight to learn from some <a href="http://consequently.org/writing/logicians/">great figures</a>, the historical figures through their writing, and my contemporaries in person, both as <em>face-to-face teachers</em> (while a student, I learned logic from Sheila Oates-Williams, Neil Williams, Rod Girle, Ian Hinckfuss, and Graham Priest), but the learning doesn’t stop when you finish your degree. I’ve learned much from colleagues (Bob Meyer, Richard Sylvan, John Slaney, Allen Hazen, Graham Priest (again), Zach Weber, Dave Ripley, Shawn Standefer), whose work I admire, and who generously share of their time at whiteboards, in seminars, and in many many conversations. I have also learned a great deal from all of my <a href="http://consequently.org/writing/logicians/">graduate students</a>, who have sent me in directions I never expected to head. If learning logic is (in part) <a href="http://consequently.org/news/2017/twelve-things-05-recognition/">gaining facility with the concepts you have</a>, as well as <a href="http://consequently.org/news/2017/twelve-things-06-expansion/">acquiring new concepts</a>, then working <em>with others</em> is a very good way to learn. The kinds of knowledge you acquire is not merely <em>knowing that</em>, but it (at least in part) skills to be learned, and they’re learned by practice, and sometimes skilled practice is best acquired when guided by others — explicitly, when the teacher knows she is <em>teaching</em> — or implicitly, when we observe an expert displaying expertise, and we can use their practice to scaffold our own, and learn by imitation. I’ve learned so much from my teachers, not only in consciously building on their ideas, but in learning how to <em>be</em> a logician by starting in their footsteps.</p>
<p>One way to develop the tradition is to <a href="http://consequently.org/class/">teach</a>, and a significant part of my job at the <a href="http://unimelb.edu.au">University of Melbourne</a> is to teach, and a lot of my time is spent teaching philosophical logic. Putting together a course is a good way of sorting out your ideas, and in philosophical logic, where the concepts very clearly and precisely build on prior ideas, it is a real intellectual challenge to see how you can teach a course in 12 weeks that, say, <a href="http://consequently.org/class/2017/PHIL30043">introduces Gödel’s incompleteness theorems</a> and everything you need to understand them. This is a challenge, and designing the curriculum in such a way to carry undergraduate students from the basics of predicate logic, through soundness and completeness, into Peano arithmetic, recursive functions, diagonalisation, and into Gödel’s proofs — and to do it in some way that there is hope that the students will survive the journey with their curiosity and interest intact! — forces you to come to grips with the concepts in a way that a cursory understanding won’t suffice. I can truly say that I’ve come to understand things much more deeply when I’ve had the opportunity to <em>teach</em> them.</p>
<p>That’s why I’m enjoying <a href="http://consequently.org/writing/ptp/">writing my new book</a>. Officially, it is a research monograph and not a textbook, but one of the ways I’ve been describing it (to myself, and to others, who ask me what I’m writing on) is that it’s trying to explain to people attracted to normative pragmatic theories of meaning what they can do with recent work in logic (in proof theory, in particular), and to explain to logicians what philosophy they should have to understand why proof theory works so well. Yes, the core of it is a particular <em>argument</em> for a way of understanding the distinctive nature of logic, but that argument is buttressed by a lot of <em>showing</em> as well as <em>saying</em>. You’ve got to <em>learn some logic</em> to understand why it is the kind of thing it is, and to get a real sense of what it can <em>do</em> (and what it can’t). To do that, is to <em>teach</em>, as well as to <em>argue</em>, and that is just how I like it.</p>
<p><em>Learning and Teaching</em> is the eleventh of <a href="http://consequently.org/news/2017/twelve-things-i-love/">twelve things that I love about philosophical logic</a>.</p>
Possibility (the tenth of twelve things I love about philosophical logic)
https://consequently.org/news/2017/twelve-things-10-possibility/
Mon, 18 Sep 2017 14:38:20 +1100https://consequently.org/news/2017/twelve-things-10-possibility/<p>In the <a href="http://consequently.org/news/2017/twelve-things-09-necessity/">previous entry</a> I explored the connection between <em>proofs</em> and <em>necessity</em>. Here, I want to spend a little time exploring the other side of the logical street, the connection between <em>models</em> and <em>possibility</em>. As I have already explained, one core insight from 20th Century work in logic is the fundamental duality between proof theory and model theory. You can define logical notions like validity by way of proofs (a <em>valid</em> argument is certified by the existence of some proof) or by way of models (an argument is shown to be <em>invalid</em> by the existence of some model which serves as a <em>counterexample</em>).</p>
<p>Exploring proofs gives you can account of the different ways that concepts are tied together. (It gives you an account of what is involved in different kinds of necessary connections. The more different proofs you have, the more connections are possible.) Approaching the validity/invalidity boundary on the other side, by way of models, gives you a very different picture of this boundary. Defining more <em>models</em> means having more <em>counterexamples</em>.</p>
<p>Model building is one very fruitful way of articulating what is — and more importantly, what <em>isn’t</em> — a part of a theory. Suppose you are interested in some strange new theory. (Put yourself back into the 19th Century, and consider a strange newfangled theory of geometry, where you accept the first four of Euclid’s axioms, but you <em>deny</em> the parallel postulate.) You’ve got your collection of basic principles, but you’re not sure what follows from them. If you can manage to build a <em>model</em> for your theory, then this can begin to address the question of what the theory involves. In particular, <em>any</em> can give you a decisive answer to some questions about what the theory <em>doesn’t</em> involve. If your model \(\mathfrak M\) gives you a way to interpret all of the basic principles of the theory as being true, and if some other claim \(A\) turns out to be <em>false</em> in \(\mathfrak M\), then you can see how \(A\) <em>doesn’t</em> follow from those basic principles. \(\mathfrak M\) gives you a picture of how the theory could be true, and in this case, it shows how \(A\) comes apart from the axioms of the theory. (So, if you think that \(A\) <em>should</em> be true, according to the theory you’re exploring, you need to supplement your axioms.)</p>
<p>Having a model on hand — in and of itself — gives you little information about what <em>does</em> follow, because theories can have more than one model, in which different things hold. If something is <em>not</em> true in a model for your theory, that tells you that it is not a consequence of the first principles theory; but when something <em>is</em> true in a model for your theory, that’s not necessarily enough to show you that it is a consequence of the first principles of the theory. After all, it might hold in <em>some</em> models, and not others. To show that something does follow (given the soundness and completeness theorems) we need to show that it holds in <em>every</em> model of the theory.</p>
<p>So, models, in and of themselves don’t do <em>everything</em>, but they are an excellent way to open up new areas of logical space. The development of models of non-Euclidean geometries helped us expand our understanding of what is involved in talk of points and lines. The development of models of different modal logics or non-classical logics helps us come to grips with different options for how basic propositional notions such as conjunction, disjunction, negation, conditionality, possibility and necessity might fit together. Models are useful tools for sketching out options.</p>
<p>So, models for theories give us powerful tools for exploring logical notions, and they provide an especially powerful way for expanding our bounds of understanding what is <em>possible</em>. Constructing a model of a theory is one way to show how that theory <em>could be true</em>. I love the way which the <em>possibility</em> of logical space is a wide plenitude, that the different antecedents for a “what if…” lead us in so many different directions.</p>
<p><em>Possibility</em> is the tenth of <a href="http://consequently.org/news/2017/twelve-things-i-love/">twelve things that I love about philosophical logic</a>.</p>
Necessity (the ninth of twelve things I love about philosophical logic)
https://consequently.org/news/2017/twelve-things-09-necessity/
Thu, 14 Sep 2017 23:55:19 +1100https://consequently.org/news/2017/twelve-things-09-necessity/<p>The next two thoughts are motivated by the two complementary aspects of contemporary research in logic, <em>proof theory</em> and <em>model theory</em>. As I try to emphasise to my students, there are two broad ways you can define logical concepts like <em>validity</em>. Following the way of <em>proofs</em>, an argument is valid if there is <em>some</em> proof leading from the premises to the conclusion. Following the way of <em>models</em>, an argument is valid if there is <em>no</em> model in which the premises are true and the conclusion is not. In proof theory, validity is vouchsafed by the existence of something: a <em>proof</em>, which certifies the claim to validity. Invalidity is the absence of such a certificate. In model theory, <em>in</em>validity is vouchsafed by the existence of something: a <em>model</em> — a <em>counterexample</em> to the claim of validity. Validity is the absence of any such counterexample. It was a great intellectual advance to understand that these are two very different ways to define logical concepts, such as validity, and it was a further advance to be able to rigorously prove that (on certain understandings of logic, such as classical first order predicate logic), these two different kinds of definitions can coincide to determine the <em>same</em> concept. A <em>soundness</em> theorem (relating an account of proofs and a account of models) shows that these two notions don’t <em>clash</em>: you never get both a proof showing that some argument is valid, <em>and</em> a model showing that it is invalid. A <em>completeness</em> theorem (also relating an account of proofs and a account of models) shows that these two notions cover the whole field — for each argument, we <em>either</em> have a proof (showing it is valid) or a counterexample (showing that it isn’t).</p>
<p>Having a sound and complete account of proofs and models for a particular understanding of validity gives you a very powerful toolkit: you can approach a question concerning validity in two distinct ways, by the way of proofs (attempting to build a bridge from the premises to the conclusions, or showing that there isn’t any) or by the way of models (attempting to show that there is a chasm between the premises and the conclusions by showing that there is some way to make the premises true and the conclusions untrue, or again, showing that there isn’t any). These two ways of accounting for validity have very different affordances, they are good for different things, both mathematically or technically, and philosophically or conceptually.</p>
<p>I am particularly interested in the kinds of conceptual gains that are possible when applying notions of proof and notions of model, and the modes of thinking that are involved when using these different tools.</p>
<p>One connection that I am beginning to learn is the intimate connection between proof and <em>necessity</em>, between logical consequence and the hardness and fixity of the logical <em>must</em>. It is one thing to think that an argument is valid, in the sense that it happens to fail to have a counterexample. It is another to have an account of <em>why</em> it is valid. What a proof gives you is some kind of account of <em>how</em> you can get from the premises to the conclusion. This kind of thing is quite powerful, especially given the generality of logical concepts. The power of concepts like conjunction, negation, the quantifiers, etc., (I think) is that our norms and rules for using them apply under the scope of suppositions (whether those suppositions are subjunctive alternatives — suppose that \(A\) had been the case — or indicative alternatives — suppose that, after all \(A\) is actually true), if we suppose that \(A\land B\) is true, it’s still totally appropriate (under the scope of that supposition) to deduce \(A\) and to deduce \(B\), the usual rules for conjunction still apply. A <em>proof</em> (on this view) from premises to a conclusion is the kind of chain of reasoning which will work under any different supposition. It shows us how the conclusion is already present, implicit in the premises. To have granted the premises is to be committed (at least implicitly) to the conclusion, and the proof renders that consequential commitment <em>explicit</em>. Of course, when confronted with a proof of an unacceptable conclusion from premises you have accepted, one appropriate response would be to reject one or another of the premises, and to resist the conclusion. That is always an option.</p>
<p>This brings logic up close to issues in <em>metaphysics</em>, in <em>epistemology</em> and in <em>philosophy of language</em>. In metaphysics, we ask questions about the ultimate nature of reality, and the bounds of what is possible, or what is necessary. Of how reality is and how it must be. The kind of necessary connection between premises and conclusion of a valid argument must bring us up to the boundary of metaphysical necessity. If something is metaphysically <em>possible</em>, then it must count as at least logically possible. If there is a way the world is that makes \(A\) true, then \(A\) cannot be logically inconsistent. If we could prove a triviality from \(A\), then this argument would apply were the world to be the way that possibility describes. Proofs in logic tell us <em>something</em> about what is necessary. (Of course, this isn’t to say that anything that is necessary is vouchsafed by a proof. That would be to say much more.)</p>
<p>Similarly, proofs can also play an <em>epistemic</em> and <em>dialogical</em> role. Provided that you and I agree on the norms governing our logical vocabulary, then if we possess a proof from \(A\) to \(B\), we agree that it’s out of bounds to accept \(A\) and reject \(B\). The proof can show us this much, to help map out the conceptual topography, see the space of possible options for us, even if we disagree on which options to take (perhaps you accept \(A\) and \(B\), and I reject both). A proof will do this work, even if we disagree on matters of necessity. Perhaps I take \(A\) to not only be false but to be <em>impossible</em>, and you take \(B\) to be <em>necessary</em>. (Such disputes are common in philosophy.) Regardless of the fact that one or other of us may be beyond the bounds of possibility, dispute here can still be rational. If, in the course of our reasoning, I begin to take your position as a live option (this is surely possible), I now have two positions before me: to accept \(A\) and \(B\), and to take them as <em>necessary</em>, or to reject \(A\) and \(B\) and to take them as <em>impossible</em>. When I do this, I can take something to be an <em>epistemic possibility</em> (a live option) which I think may also be metaphysically <em>impossible</em>. When we use the tools of <em>proofs</em>, we have guides to help see what positions are open to us, even if this does not tell us the whole story of which position may be best to take.</p>
<p>I love the way in which the <em>necessity</em> of the logical <em>must</em> brings us right up to concerns of metaphysics and epistemology, of the nature of reality and what options we have as we attempt to understand it.</p>
<p><em>Necessity</em> is the ninth of <a href="http://consequently.org/news/2017/twelve-things-i-love/">twelve things that I love about philosophical logic</a>.</p>