Knowing the Natural Law: From Precepts and Inclinations to Deriving Oughts by Steven J. Jensen (review)

This important book is an account of how we know the natural law. It aims to be substantially Thomistic. This means, first and foremost, that it bases the knowledge of natural law on a knowledge of nature. Of course, many secular ethicists find no value in nature (as they conceive it) and reject the very idea of natural law. But for a while now, some Catholic moralists have been trying to save natural law by denaturing it, that is, by disengaging the knowledge of it from knowledge of nature. Jensen finds the upshot partly mystifying, partly just confused. His main target is the New Natural Law theory (hereafter NNL) of Germain Grisez and John Finnis, with its hard is-ought dichotomy, its wide disconnect between practical and speculative reason, and its flat denial of a single final human end. Jensen also works to forestall the charges of physicalism that Martin Rhonheimer might raise.

Jensen lays out his argument in ten very logically structured chapters, and he executes it with his typical blend of clarity, pedagogical skill, and gentle irony. He is very deft at dealing with the side issues that emerge along the way without losing or entangling the main thread. Besides Aquinas and a few Thomists, he draws a good deal on Peter Geach and even more on Phillipa Foot. It is a handsome volume. I have one small editorial gripe: views are sometimes ascribed to authors without documentation. To me, the utility of such documentation would have offset the extra bits of clutter.

Chapter 1 presents the issues. Chapter 2 studies the relevant lines of Thomas's famous natural-law text Summa theologiae I-II, q. 94, a. 2. Jensen finds that it makes knowledge of goods a function of knowledge of natural inclinations. He also gathers from it various ways in which one piece of knowledge can be a function of, or directly derive from, another. Syllogistic derivation is only one way. So even if, as NNL theorists insist, conclusions containing ought cannot derive from premises lacking it, ought-judgments may still derive, quite rationally, from is-judgments.

The rest of the book is about how we move from inclinations to goods, from goods to oughts, and from oughts to actions. Jensen frames it all, very effectively, in terms of the four types of knowledge that Thomas distinguishes in STh I, q. 14, a. 16: purely speculative, practical in matter but speculative in mode (Jensen calls this materially practical), practical also in mode but not in end (virtually practical), and practical also in end (fully practical). So, first, Jensen works to identify a purely speculative knowledge underlying the knowledge of natural-law precepts. It is some sort of knowledge of some sort of natural inclinations. Thomas is not too explicit about either sort, and Jensen is cautious, devoting three chapters to the matter. Eventually he centers on a text that seems to tie at least some knowledge of human good to a grasp of the intellect's intrinsic, nonconscious inclination toward truth. His own thesis is that the knowledge of the human good as a whole, upon which rests the knowledge of natural law as a whole, derives from knowledge of the nonconscious inclinations of our whole set of vital powers. This starts from perception of the powers' spontaneous workings.

Knowledge of the human good is at least materially practical. Against NNL theory, Jensen argues forcefully, with some help from Geach and Foot, that such knowledge is nonetheless descriptive. It is simply knowledge of human teleology. The true good of a natural being is nothing other than the perfection of its nature, seen as an object to which it is naturally inclined. Jensen uses the appeal to nonconscious inclinations and their objects to rebut Finnis's argument that we know human nature only in light...