more from Timothy Williamson

Single Idea 14626

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

Full Idea

In system S5 matters of possibility and necessity are always non-contingent.

Gist of Idea

In S5 matters of possibility and necessity are non-contingent

Source

Timothy Williamson (Modal Logic within Counterfactual Logic [2010], 3)

Book Reference

'Modality', ed/tr. Hale,B/Hoffman,A [OUP 2010], p.91


A Reaction

This will be because if something is possible in one world (because it can be seen to be true in some possible world) it will be possible for all worlds (since they can all see that world in S5).