’s own George H. Smith reviews “one of the best introductions to natural law available.”

George H. Smith was formerly Senior Research Fellow for the Institute for Humane Studies, a lecturer on American History for Cato Summer Seminars, and Executive Editor of Knowledge Products. Smith’s fourth and most recent book, The System of Liberty, was published by Cambridge University Press in 2013.

As a moral foundation for libertarianism, natural law is a mixed blessing. In its various manifestations throughout history, natural law theory has been used to “justify” oligarchy, feudalism, theocracy, and even socialism. In fact, until the advent of political individualism in the seventeenth century, natural law was linked to an organismic view of society and was used to dictate the role or function of the individual within the structure of society as a whole. It was not until natural law evolved into a theory of natural rights that “nature,” to quote the historian Basil Wiley, “ceases to be mainly a regulating principle, and becomes mainly a liberating principle.”

Thus, when libertarians claim that coercion is contrary to natural law (or to the nature of man), they must realize that, aisde from the truth or falsity of this assertion, such an appeal to “nature” places them in a confused and nebulous political tradition. It was this confusion, coupled with the seeming ability to “justify” anything with reference to natural law, that made modern assaults on natural‐​law theory so persuasive to many philosophers. It is for this reason that libertarians must do their homework carefully when venturing into the twisted pathways of natural law theory, and an excellent place to begin is Paul Sigmund’s Natural Law in Political Thought.

Natural law theorists, writes Sigmund, share a common belief “in the ability of human reason to deal with moral problems.” More specifically, natural law entails “the belief that there exists in nature and/​or human nature a rational order which can provide intelligible value‐​statements independently of human will, that are universal in application, unchangeable in their ultimate content, and are morally obligatory on mankind.” This belief recurs throughout the history of political thought “because it seems that man can never give up the search for a rational justification of political and moral values.”

While natural law is primarily a moral doctrine, its application to political theory has consisted, in essence, of the claim that there exists over and above man‐​made (positive) law, a higher, objective law by which positive law can be judged—a law or principle, in other words, rooted somehow in the “nature of things.” Contrary to legal positivism, where the ultimate justification for law lies in its promulgation by a political authority, natural law theorists have denied to the state the ability to create law ex nihilo. Instead, positive law must conform to the requirements of natural law, from whence it derives its moral force.

Paul Sigmund examines virtually every major figure, whether philosopher or legal theorists, who falls within this general frame of reference, and he does so with great clarity and ease of style. Included here are such diverse thinkers as Plato, Aristotle, the Stoics, Cicero, the medieval canonists, Acquinas, Ockham, Suarez, Grotius, Hooker, Hobbes, Locke, and the American Founding Fathers. Also included are various critics of natural law, such as Jeremy Bentham, who referred to the doctrine of natural rights as “nonsense upon stilts.”

Although primarily expository in intent, Natural Law in Political Thought is not without controversial interpretations. For example, Sigmund wishes to draw into the natural‐​law camp such questionable figures as Rousseau, Burke, Kant, and Marx. The first two philosophers can plausibly, if problematically, be interpreted in this manner, but to interpret the latter two in this way appears to me quite fantastic: Since, for Kant, the real or “noumenal” world is closed to man’s comprehension, I fail to see how he could in any sense be said to ground his moral theory in the nature of man or the world. The Thomistic interpretation of Kant as representative of the formal destruction of natural‐​law theory is certainly the more accurate view.

As for Marx, his advocacy of economic determinism, under which economic conditions control one’s philosophy rather than vice‐​versa, renders any kind of moral stance on his part superfluous (not to mention contradictory) to his basic viewpoint. And this eliminates the possibility of placing Marx in the natural law tradition. While it may be true, as Sigmund says, that “for all his pretense at being a scientist, Marx was fundamentally a moralist,” this evaluation surely undercuts the entire purpose of the Marxian system.

Despite my strong disagreement on these points, I can easily recommend Natural Law in Political Thought as one of the best introductions to natural law available today. Libertarians will find it a valuable source of information from which they will hopefully build a clear and systematic political theory. Reviewed by George H. Smith / Political Philosophy (214 pages) / LR Price $4.95