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 Reference
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?