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Single Idea 16958

[filed under theme 4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / g. System S4 ]

Full Idea

In S4 logic the actual world is, in itself, special, not just from our point of view.

Gist of Idea

In S4 the actual world has a special place

Source

Michael Dummett (Could There Be Unicorns? [1983], 8)

Book Ref

Dummett,Michael: 'The Seas of Language' [OUP 1993], p.348

A Reaction

S4 lacks symmetricality, so 'you can get there, but you can't get back', which makes the starting point special. So if you think the actual world has a special place in modal metaphysics, you must reject S5?

The 7 ideas with the same theme [version imposing two conditions on accessibility]:

15544 If what is actual might have been impossible, we need S4 modal logic [Armstrong, by Lewis]
14972 S4 has 14 modalities, and always reduces to a maximum of three modal operators [Cresswell]
16958 In S4 the actual world has a special place [Dummett]
14671 What is necessary is not always necessarily necessary, so S4 is fallacious [Salmon,N]
9747 The system S4 has the 'reflexive' and 'transitive' conditions on its accessibility relation [Fitting/Mendelsohn]
7794 There are seven modalities in S4, each with its negation [Girle]
15102 S4 says there must be some necessary truths (the actual ones, of which there is at least one) [Cameron]