Why are counterfactual claims taken seriously by philosophers? Aren't they just an imaginative way of thinking and talking? For example, why is a counterfactual of the form "If it had been the case that A, then it would be the case that C" supposed to have truth conditions? For if causal determinism is true, then there is a complete specification W of the history of world w in which A would occur such that W entails either the truth of C or the falsity of C, making the counterfactual either vacuously true or a contradiction (and this is so for all possible deterministic worlds which include A); whereas if causal determinism is not true, then the history of w cannot be fully specified because A depends on non-deterministic processes, and the truth or falsity of the counterfactual is not determined. And for a non-deterministic world of which the history is fully specified (i.e. W includes the outcomes of non-deterministic processes) in which A occurs, the vacuous/contradictory result again obtains.
Isn't the Lewis/Stalnaker account thus just an attempt to apply logical rigor to a non-rigorous way of thinking-- namely, the everyday talk of counterfactuals that invokes a sort of imaginary time travel?