Single Idea 16953

[catalogued under 4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / a. Systems of modal logic]

Full Idea

If T is only possible if S obtains, T and S hold in the actual world, and S does not obtain in world v possible relative to the actual world, then the actual is not possible relative to v, since T holds in the actual. Accessibility can't be symmetrical.

Gist of Idea

Relative possibility one way may be impossible coming back, so it isn't symmetrical

Source

Michael Dummett (Could There Be Unicorns? [1983], 1)

Book Reference

Dummett,Michael: 'The Seas of Language' [OUP 1993], p.330


Related Idea

Idea 16952 If something is only possible relative to another possibility, the possibility relation is not transitive [Dummett]