Full Idea
For counterfactuals there is the 'nomic-derivational' approach (which logically derives them from laws), and the 'possible world' approach (based on truth in worlds close to the actual one).
Gist of Idea
Counterfactuals are either based on laws, or on nearby possible worlds
Source
report of Jaegwon Kim (Philosophy of Mind [1996], p.141) by PG - Db (ideas)
Book Reference
Kim,Jaegwon: 'Philosophy of Mind' [Westview 1998], p.141