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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 Ref
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]
| 16952 | If something is only possible relative to another possibility, the possibility relation is not transitive [Dummett] |
| 16953 | Relative possibility one way may be impossible coming back, so it isn't symmetrical [Dummett] |
| 16951 | It was realised that possible worlds covered all modal logics, if they had a structure [Dummett] |
| 16954 | Generalised talk of 'natural kinds' is unfortunate, as they vary too much [Dummett] |
| 16956 | To explain generosity in a person, you must understand a generous action [Dummett] |
| 16960 | If possibilitiy is relative, that might make accessibility non-transitive, and T the correct system [Dummett] |
| 16958 | In S4 the actual world has a special place [Dummett] |
| 16957 | Possible worlds aren't how the world might be, but how a world might be, given some possibility [Dummett] |
| 16959 | If possible worlds have no structure (S5) they are equal, and it is hard to deny them reality [Dummett] |