 Timothy Williamson (2007: Chap. 5) studies the epistemology of counterfactual, or subjunctive, conditionals. He points out their role in contingency planning and decision making. According to his account, one learns a subjunctive conditional if one robustly obtains its consequent when imagining its antecedent. Experience disciplines imagination. The experience leading to a judgment that a subjunctive conditional holds may be neither strictly enabling nor strictly evidential so that knowledge of the conditional is neither purely a priori nor purely a posteriori. Williamson claims that knowledge of subjunctive conditionals is foundational so that decision theory appropriately grounds knowledge of an act’s choiceworthiness in knowledge of such conditionals.