 Aquinas’s repeated affirmation that practical reason’s first principles are undeduced refutes the common accusation or assumption that his ethics invalidly attempts to deduce or infer ought from is, for his affirmation entails that the sources of all relevant oughts cannot be deduced from any is. There remain, however, a number of contemporary Thomists who deny that such a deduction or inference need be fallacious, and regard Aquinas as postulating some such deduction or inference. They are challenged., however, by others (such as Rhonheimer, Boyle, and Finnis) who, while sharing the view that his ethics is in these respects fundamentally sound, deny that Aquinas attempted or postulated any such deduction or inference, and ask for some demonstration (i) that he did and (ii) that he or anyone else could make such a deduction or inference.