Full Idea
A clarifying assumption is that if something might be true, then it might be true in some particular way. …Possible worlds begin from this, and the assumption that what might be true can be described as how a possibility might be realised.
Gist of Idea
If it might be true, it might be true in particular ways, and possible worlds describe such ways
Source
Robert C. Stalnaker (Reference and Necessity [1997], 2)
Book Reference
Stalnaker,Robert C.: 'Ways a World Might Be' [OUP 2003], p.170
A Reaction
This is a leading practitioner giving his best shot at explaining the rationale of the possible worlds approach, addressed to many sceptics. Most sceptics, I think, don't understand the qualifications the practitioners apply to their game.
Related Idea
Idea 16398 Possible worlds allow discussion of modality without controversial modal auxiliaries [Stalnaker]