Full Idea
A possible world isn't a distant country that we are coming across, or viewing through a telescope. …A possible world is given by the descriptive conditions we associate with it. …Possible worlds are stipulated, not discovered by powerful telescopes.
Gist of Idea
Possible worlds aren't puzzling places to learn about, but places we ourselves describe
Source
Saul A. Kripke (Naming and Necessity lectures [1970], Lecture 1)
Book Reference
Kripke,Saul: 'Naming and Necessity' [Blackwell 1980], p.44
A Reaction
His point is that it is absurd to be puzzling over the identity of what exists in some possible world, because the world is specified by us. If I say 'Nixon might have been a frog', I must be referring to Nixon. The problem is whether it is true.