The University of Manchester, Anthony Paul Wheatley, For the degree of Doctor of Philosophy, In Defence of Neo-Scholastic Ethics: A Critique of Finnis and Grisez's New Natural Law Theory, 2015In a major contribution to Neo-Aristotelian ethics, John Finnis and Germain Grisez have argued that foundational moral principles - or 'the first principles of practical reason' - are self-evident and cannot be derived from facts about human nature. This claim sets Finnis and Grisez against the older, Neo-Scholastic interpretation of natural law theory, which states that fundamental moral truths can be derived from an Aristotelian philosophy of nature. More significantly, Finnis and Grisez have claimed that Aquinas accepted a version of the fact-value distinction and the impossibility of deriving normative conclusions from theoretical or factual premises later defended by Hume.In this thesis, I argue to the contrary that the first principles of practical reason are grounded in truths of natural philosophy. Furthermore, I argue that, for Aquinas, morally significant truths can indeed be derived from a consideration of man's faculties and their proper functioning. I also argue that, pace Finnis and Grisez, a Neo-Scholastic hierarchy of the basic goods is not incompatible with their incommensurability. It is my contention, then, that Finnis and Grisez's new natural law theory constitutes a misinterpretation of Aquinas's moral philosophy and the relationship between theoretical and practical reason in Aristotelian philosophy.I argue that the first principles of practical reason are self-evident, but show that such self-evident truths are, for Aquinas, more akin to a posteriori necessary truths. Our grasp of a self-evident truth, then, will depend upon our prior grasp of the nature to which the self-evident truth refers. I then argue that, according to Aquinas, metaphysics and natural philosophy provide explanatory justifications for the first principles of practical reason. The Aristotelian will ground these first principles by reference to an Aristotelian philosophy of nature. I argue that, pace Finnis and Grisez, Aquinas holds that we can derive significant moral truths from facts about our faculties and about human nature in general.I argue that Hume's no-is-from-ought principle is not a general law of logic, which is applicable to any attempt to derive a normative conclusion from factual premises. Instead, I argue that it is licit to derive a normative conclusion from truths employing functional concepts. However, I also argue that functional concepts and Aristotelian categoricals can tell us only what an instance of its kind must do if it is to count as a good instance. They cannot tell us whether we have reason to be a good instance of our kind. To answer that question, we must grasp that being a good human being is a means to acquiring the basic goods. Finally, I argue that the concept of a function has normative and evaluative dimensions. This view of functions is incompatible with Finnis and Grisez's understanding of theoretical reason, according to which, theoretical reason is concerned with 'bare facts', where 'bare facts' are taken to exclude all normative and evaluative elements. I contend, then, that Finnis and Grisez err by assuming that all facts must, by their nature, exclude normative and evaluative elements.