 The need for such a counterfactual formulation raises several questions that will be explored in more detail below. First, how should one understand (what is the appropriate interpretation of or semantics for) the counterfactuals in question? Without attempting to answer this question in detail, it seems plausible that if interventionist counterfactuals are to be useful in elucidating causal claims, their semantics must be different from the familiar Lewis/Stalnaker possible world semantics in some respects, as is argued by Woodward (2003), Briggs (2012), Fine (2012). For example, on the Lewis/Stalnaker semantics, counterfactuals with logically or metaphysically impossible antecedents are always vacuously true, but presumably we don’t want the causal claims that might be associated with such counterfactuals to be automatically true (cf.  §12).  