Full Idea
The idea of 'impossible worlds' was introduced into epistemic logic.
Gist of Idea
Epistemic logic introduced impossible worlds
Source
Horsten,L/Pettigrew,R (Mathematical Methods in Philosophy [2014], 4)
Book Reference
'Bloomsbury Companion to Philosophical Logic', ed/tr. Horsten,L/Pettigrew,R [Bloomsbury 2014], p.19
A Reaction
Nathan Salmon seems interested in their role in metaphysics (presumably in relation to Meinongian impossible objects, like circular squares, which must necessarily be circular).