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If the gap between the first two levels or concepts of natural law is fairly small, the
differences between those two concepts and this one are very substantial. The common
substantive content of classic natural law theories–the emphasis on natural teleology, virtue, and
practical wisdom–on this understanding of natural law is much broader. This is not surprising,
given that Aquinas’s thought is, after all, characterized as “Christian Aristotelianism.” The
commentaries on Aristotle form an important part of his corpus of writing, and Aristotle is, for
him, “the Philosopher.” Still, there remain important differences between the philosophy of
Aquinas and that of Aristotle. Some of these differences concern the role of revelation (for
example, the inclusion of divine positive law in Aquinas's typology of law) and others are
perhaps differences that can be argued about even within Aristotle’s own framework of reason
(e.g., the difference between Aristotle’s Prime Mover and Aquinas’s Creator).
Classical (Thomistic) Natural Law
The fourth and most determinate sense of natural law, strictly or properly speaking, is
classical Thomistic natural law. On this view, human beings flourish and achieve such
happiness as is possible in this life by living good lives, following a law inscribed in their being.
The good life is understood, in particular, as a life of virtue and excellence, grounded in
intellectual and moral virtue. They choose particular ways of living well, guided by the self-
evident basic principles of natural law, which they grasp through practical reason and by right
desire (the fruit of proper habituation).
Thomas describes the natural law as the rational creature’s “share of the Eternal Reason,
whereby it has a natural inclination to its proper act and end; and this participation of the eternal
Convention