Full Idea
If our space of possible worlds has no structure, as in the semantics for S5, then, from the standpoint of the semantics, all possible worlds are on the same footing; it then becomes difficult to resist the claim that all are equally real.
Gist of Idea
If possible worlds have no structure (S5) they are equal, and it is hard to deny them reality
Source
Michael Dummett (Could There Be Unicorns? [1983], 8)
Book Reference
Dummett,Michael: 'The Seas of Language' [OUP 1993], p.348
A Reaction
This is a rather startling and interesting claim, given that modern philosophy seems full of thinkers who both espouse S5 for metaphysics, and also deny Lewisian realism about possible worlds. I'll ponder that one. Must read the new Williamson….