*Abstract*: In this talk, I provide two different models for a theory of grounds meeting the following desiderata:\(\def\yright{\succ}\)

*Grammar*: There are objects, which we call*grounds*, which can be grounds*for*propositions or grounds*against*propositions.*Derivation*: A derivation of a sequent \(X\yright A,Y\) gives us a systematic way to construct a ground*for*\(A\) 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*against*\(A\) 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 \(A\).*Interpretation*: This theory can be interpreted in an*epistemic*sense, where grounds are our means to access the truth or falsity of a proposition, or a*metaphysical*sense, where grounds show how a proposition is made true by the world.*Grasp*: Grounds are the kinds of things we can*possess*.*Hyperintensionality*: Not every ground is a ground for every tautology. A ground for \(A\) need not also be a ground for each logical consequence of \(A\).*Structure*: 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 \(A\).

The result is a model of grounds with significant similarities to the BHK interpretation of constructive logic, but for the classical sequent calculus.

This is a talk for the Melbourne Logic Seminar.

I’m *Greg Restall*, and this is my personal website. ¶ From August 2021, I will be the Shelby Cullom Davis Professor of Philosophy at the University of St Andrews.

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