I’d like to guage some philosophical opinions. (I don’t have many of my own. Most of them have been worn down by years of logical abuse.)

First, some pre-requisites:

Let’s understand ‘possibly’ as a

*metaphysical*sort of possibility. If it helps, think of it as truth in some possible world, no matter how outlandish.Let’s understand

*a priori knowledge*in the way that all of the people who talk about*a priori*knowledge understand the term. Plausibly, we can’t know that Hesperus is Phosphorus*a priori*, but, plausibly, we can know the Chinese Remainder Theorem*a priori*.

Here’s the question. Can we have *a priori* knowledge of any proposition of the form

possibly ~

p

where *p* is true? (We don’t need to know *a priori* that *p* is true.) Speaking rather briskly, do we have *a priori* knowledge that fatalism is false? (Where ‘fatalism’ is the thesis that everything that is true is metaphysically necessary.) This is fudging a scope distinction, commuting a propositional quantifier under the knowledge operator, but that doesn’t seem like *too* much of a worry. If you think that there’s a proposition ‘@’ true in the actual world alone (of any of the possible worlds accessible from the actual world) then, the question reduces to this:

Can we know

a priorithat possibly ~@?

What do *you* think? What do the *Standard Positions* on these topics (*a priori* knowledge, necessity, semantics, etc.) say about this? Is there anything that we obviously have *a priori* knowledge of that clearly *a priori* entails possibly ~@? (That’d be interesting: I can’t think of any examples right now…)

Anyway, if you’re the kind of person to have opinions on these sorts of issues, let me know what you think in the comments.

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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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