 This characterization makes explicit reference to conditions that must be satisfied by the intervention variable \(I.\) Although perhaps not mandatory, questions about what it means for such an \(I\) to be possible and how we are to understand the antecedents of the associated interventionist counterfactuals (“If an intervention satisfying  (M1)–(M4)  on \(X\) were to occur,…”) thus arise in a natural way on this characterization—or at so I will assume in what follows. 