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Ideas for 'Dialectic of Enlightenment', 'What Required for Foundation for Maths?' and 'Logical Necessity'

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4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / h. System S5

12204	The logic of metaphysical necessity is S5 [Rumfitt]
	Full Idea: It is a widely accepted thesis that the logic of metaphysical necessity is S5.
	From: Ian Rumfitt (Logical Necessity [2010], §5)
	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.