compositionality See COGNITIVE SCIENCE, PHILOSO-. PHY OF LANGUAG. compossible, capable of existing or occurring together. E.g., two individuals are compossible provided the existence of one of them is compatible with the existence of the other. In terms of possible worlds, things are compossible provided there is some possible world to which all of them belong; otherwise they are incompossible. Not all possibilities are compossible. E.g., the extinction of life on earth by the year 3000 is possible; so is its continuation until the year 10,000; but since it is impossible that both of these things should happen, they are not compossible. Leibniz held that any non-actualized possibility must be incompossible with what is actual. See also PRINCIPLE OF PLENITUDE. P.Mac.