Full Idea
Two possibilities are incompatible when no possibility determines both.
Gist of Idea
If two possibilities can't share a determiner, they are incompatible
Source
Ian Rumfitt (The Boundary Stones of Thought [2015], 7.1)
Book Reference
Rumfitt,Ian: 'The Boundary Stones of Thought' [OUP 2015], p.185
A Reaction
This strikes me as just the right sort of language for building up a decent metaphysical picture of the world, which needs to incorporate possibilities as well as actualities.
Related Ideas
Idea 18826 'True at a possibility' means necessarily true if what is said had obtained [Rumfitt]
Idea 18829 The truth grounds for 'not A' are the possibilities incompatible with truth grounds for A [Rumfitt]