Single Idea 15131

[catalogued under 4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / h. System S5]

Full Idea

In S5, necessity and possibility are not themselves contingent matters. This is plausible for metaphysical modality, since metaphysical possibility, unlike practical possibility, does not depend on the contingencies of one's situation.

Gist of Idea

If metaphysical possibility is not a contingent matter, then S5 seems to suit it best

Source

Timothy Williamson (Truthmakers and Converse Barcan Formula [1999], §1)

Book Reference

-: 'Dialectica' [-], p.255


A Reaction

This is the clearest statement I have found of why S5 might be preferable for metaphysics. See Nathan Salmon for the rival view. Williamson's point sounds pretty persuasive to me.