Counterfactual conditionals aren’t truth-functions of their antecedents and consequents. If the consequent counterfactually follows from the antecedent, in general, it would not be because there is an entailment from A to C, but because there is a sort of entailment from A conjoined with other propositions that are, in some sense, implicitly assumed along with A. In “The Problem of Counterfactual Conditionals” (in Fact, Fiction, and Forecast, 4th ed.) Goodman calls these other propositions the “relevant conditions” of the counterfactual, and says that one of the main philosophical problems with counterfactuals is the explicit specification of relevant conditions. I think I agree thus far.
Goodman also says, however, that the sense in which the relevant conditions are implicitly assumed is that they are taken to be true in the actual world. In Goodman’s words: “in asserting the counterfactual, we commit ourselves to the actual truth of the statements describing the requisite relevant conditions” (8). This part I’m not sure about. My worry is that this stand on speakers’ attitudes towards relevant conditions cannot account for certain counterfactuals related to utterly non-actual states of affairs. Take Irish Jim, who occupies a world in which the Irish can fly. In this world, the Irish are unlike other human beings in this respect, and they can fly strictly in virtue of their Irishness. Now consider:
(1) If Jim weren’t Irish, he couldn’t fly.
This counterfactual seems as true to me as any other counterfactual, and it sure looks to me like one of its relevant conditions is that:
(2) All Irish people can fly.
But, of course, I don’t believe (2). Since it seems that my beliefs about (1) and the powers of the Irish don’t seem to be inconsistent, it seems that the sense in which (1) implicitly assumes (2) is not that it assumes that (2) is actually true.
But perhaps (2) is not a relevant condition of (1), and (1) doesn’t implicitly assume (2) in any sense at all. Perhaps the relevant condition that I wanted to capture by (2) is something more like:
(3) In Jim’s world, all Irish people can fly.
Now, (3) I actually do believe (to the extent that I believe in facts about non-actual worlds), and (3) seems to do all the work that (2) can do in making (1) come out true. And, strictly speaking, I guess that (3) is true just in case (3) is true in the actual world – i.e., just in case, in the actual world, it is true that, in Jim’s world, all Irish people can fly. Furthermore, in general, I suppose, one believes that (3) is true just in case one believes that (3) is true in the actual world. So, if (3) is a relevant condition of (1), it looks like a speaker of (1) assumes (3) to be actually true. So, strictly speaking, maybe Goodman is right about speakers’ attitudes towards relevant conditions – they assume that relevant conditions are actually true. But if, as Goodman suggests at a certain point (6f), we want the relevant conditions to be non-modal, then (3) won’t do. In that case, I am convinced that we would do better to say that (2) is a relevant condition of (1), and rethink the nature of speakers’ attitudes towards the relevant conditions of counterfactuals that they utter.
I want to say that the attitude of the speaker towards the relevant conditions is one of something like provisional acceptance, or acceptance for the sake of argument. I can’t think of a good reason not to endorse this view, and I think it clearly has important consequences (different from those of Goodman’s view) for how we should approach both the problem of specifying relevant conditions and the problem of understanding the illocutionary force of utterances of counterfactual conditionals.