 Aquinas’ moral and political philosophy has to be reconstructed from his theological treatises and commentaries and his commentaries on Aristotle’s Nicomachean Ethics and the first two and half books of Aristotle’s Politics. Its proper interpretation has been a matter of some difficulty from the time of his death in 1274. In recent decades the way to understand some aspects of its foundational concepts and logic has been strenuously disputed, not least among those philosophers who see it as offering a broadly sound answer to radical scepticism about value and obligation, an answer truer and more human than Kant’s or Bentham’s or their (in the broadest sense) successors’. A partial sample of these controversies is given in 1.1 and 1.2 below, which state the more common interpretation on two strategic issues and then elaborate objections to those interpretations. The remainder of this article then proceeds on the basis that there is merit in these objections, and that the study of Aquinas’ ethics as a systematic and strictly philosophical work of practical reason (at its most general and reflective) is still in its infancy. Further textual support, from over 60 of Aquinas’ works, can be found in Finnis 1998. Criticisms of the interpretation of Aquinas’ theory that is proposed in that work can be found in Paterson 2006, Wheatley 2015, Long 2004, and earlier in Lisska 1998 and McInerny 1997. These works argue in various ways that that interpretation denies or neglects the metaphysical foundations of the principles of practical reason that it offers to identify. Support, in general, for the approach in this article will be found in Rhonheimer 2012 and 2000. The first issue underlying this debate is whether the order of inquiry and coming to know (the epistemological order) is the same as the order of metaphysical dependence. The second issue is whether we can settle the first issue by using the epistemological axiom that we come to an (ultimately metaphysical) understanding of dynamic natures by understanding capacities through their actuations – which, in turn, we come to understand by understanding their objects. Does or does not that axiom entail that understanding of objects such as the intelligible goods (the objects of acts of will) precedes an adequate knowledge of nature, notwithstanding that (as is agreed on all sides) in the metaphysical order of intrinsic dependence such objects could not be willed or attained but for the given nature of (in this case) the human person?