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Single Idea 12204

[from 'Logical Necessity' by Ian Rumfitt, in 4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / h. System S5 ]

Full Idea

It is a widely accepted thesis that the logic of metaphysical necessity is S5.

Gist of Idea

The logic of metaphysical necessity is S5

Source

Ian Rumfitt (Logical Necessity [2010], §5)

Book Reference

'Modality', ed/tr. Hale,B/Hoffman,A [OUP 2010], p.61


A Reaction

Rumfitt goes on to defend this standard view (against Dummett's defence of S4). The point, I take it, is that one can only assert that something is 'true in all possible worlds' only when the worlds are all accessible to one another.