<i>Is</i> and <i>Ought</i> in Aquinas

John Finnis

in Reason in Action

Published in print April 2011 | ISBN: 9780199580057
Published online September 2011 | e-ISBN: 9780191729379 | DOI:
Is and Ought in Aquinas

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Natural inclinations are not the ground of the truth or intelligibility of practical reason's first principles, which direct us to the basic aspects of human flourishing. But inclinations are proximate to the nature which is the ontological ground of the truth of those principles, whose epistemological basis, however, is the goods (perfections) which we understand in understanding those principles. For the nature of a dynamic reality is understood by knowing its capacities, which are understood by knowing their actuations, which are understood by knowing their objects — which in the case of humanly willed acts are the intelligible intrinsic basic goods. Along these lines we can then understand why Aquinas insisted on the indemonstrability of practical first principles, that is, on the non-derivability of ought from is. This chapter proceeds by a close study of relevant passages in Aquinas on first principles, and on the transition from these to moral precepts.

Keywords: Aquinas; natural inclinations; practical reason; first principles; epistemological grounds; ontological grounds; indemonstrability

Chapter.  6123 words. 

Subjects: Jurisprudence and Philosophy of Law

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