Full Idea
If some worlds are metaphysically impossible, it seems that we could never know it. By assumption the information is not available a priori, and a posteriori information only tells us about our world.
Gist of Idea
How can we know the metaphysical impossibilities; the a posteriori only concerns this world
Source
David J.Chalmers (The Conscious Mind [1996], 2.4.2)
Book Reference
Chalmers,David J.: 'The Conscious Mind' [OUP 1997], p.137
A Reaction
You need essentialism to reply to this. If you discover the essence of something, you can predict its possibilities. You discover the natures of the powers and dispositions of actuality.
Related Idea
Idea 16425 Metaphysical necessity is a bizarre, brute and inexplicable constraint on possibilities [Chalmers]