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Single Idea 16951

[filed under theme 4. Formal Logic / D. Modal Logic ML / 1. Modal Logic ]

Full Idea

The new discovery was that with a suitable structure imposed on the space of possible worlds, the Leibnizian idea would work for all modal logics.

Gist of Idea

It was realised that possible worlds covered all modal logics, if they had a structure

Source

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

Book Ref

Dummett,Michael: 'The Seas of Language' [OUP 1993], p.329


The 9 ideas from 'Could There Be Unicorns?'

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