Lewis makes the appeal of possible worlds to counterfactual language. I think this is something interesting. “If my parents didn’t copulate, then I wouldn’t exist”. This is a true statement. The fact of the matter (lets just say this happened to be true as a logical possibility) is that my parents did copulate, and I am here; furthermore, it is because my parents engaged in copulation that I am alive today.
It is not the case that my parents didn’t copulate, and it is not the case that I don’t exist (indexical to the time of writing). A counterfactual posits, as its conditional statement, a factually false proposition as the antecedent claim (the antecedent claim being ‘if my parent’s didn’t copulate…’); and somehow leading to a true consequent.
How is this possible? It is possible (non-technical sense) because is conceivable; and if it is conceivable, it is possible. Possible worlds semantics allows for the legitimacy of counterfactual language. I suspect a very transcendental move here. Could we read Lewis as saying possible worlds ontology is the only way we can understand counterfactual semantics?
If so; he’s in good company of making very interesting appeals to metaphysical facilities in virtue of the very possibility of experience. Well done, Lewis…