As all later Russian fiction came out of Gogol’s The Overcoat, so Anglo-American moral philosophy in the 20th century came out of G. E. Moore’s Principia Ethica, published in 1903. By inventing the “naturalistic fallacy,” Moore made canonical the split between Is and Ought first suggested by Hume. The fact/value dichotomy became dogma. No more could one appeal to the features of a thing—the facts—to explain the commendation or condemnation of it: “good” and “bad” became unmoored from natural properties. Anything whatsoever could be called good, or bad, since such evaluations had nothing to do with what the things are. So what, if anything, did “good” mean if not the natural properties of the good thing? The history of analytic moral philosophy could be told in terms of the successive answers to this question through the century. Despite Peter Geach’s important reminder about attributive and predicative adjectives, the divorce of good from the things called good was not repaired. In the end, the dominant view, as Alasdair MacIntyre has said, was Emotivism. “Good” and “bad” signified the feelings I have when I evaluate, feelings which are not dictated by the inherent qualities of things I call good or bad. Condemning something was like admitting to a toothache. Calling something good was confessing that one enjoyed it.

For decades this silliness was confined to the academy and ordinary folks were unaffected by it. But, as ideas eventually will, the fact/value split drifted into the wider culture and Universal Emotivism was established, something that can be verified in almost any issue of a newspaper, in op-ed articles and letters to the editor. Standing athwart this is J. Budziszewski’s magnificent book What We Can’t Not Know.

That such a book had to be written tells us something of the pass to which we have come. That human beings have the capacity to know a good deal about themselves and the world is a contention, really a simple observation, that has been under attack for centuries. Once, it was taken for granted that men and women know the difference between good and evil, that there is a difference to know, and that philosophy assumes rather than contests this. Unsurprisingly, when that common knowledge was rejected, theories tended to insist that there was nothing to know about good and evil.

It is moral knowledge that Budziszewski, an associate professor of government and philosophy at the University of Texas, is principally concerned with, but he does not regard such knowledge as unanchored in knowledge of the physical world and our own makeup. His subject is natural law and you may wonder why he doesn’t just say so. He doesn’t because he insists on a distinction that is either blurred or forgotten in many discussions, between what everybody can be expected to know and theories which explain or account for such knowledge. In short, there are the moral truths human beings naturally know and a theory about those truths; it is usually the latter that is meant by natural law.

One of the many merits of the book is that it clearly makes that distinction between the theory and content of natural law. Once made, Budziszewski’s discussion must of course be located on the theoretical side of the divide. Unsurprisingly, he is guided by Thomas Aquinas in many matters and this book is complementary to Russell Hittinger’s recent study The First Grace: Rediscovering the Natural Law in the Post-Christian World. Among the issues that confront Budzisewski are the following: Why is a work of theology—the Summa Theologiae—the best source for the view that there are certain moral truths anyone, believer or not, already holds? How precisely linked to theism is this common knowledge? How is it possible to forget what one nonetheless knows? Nothing is more familiar than the charge that opposition to abortion is a religious stance and therefore cannot be invoked in a supposedly secular environment. Often this opposition is said to be Roman Catholic, the implication being that it has bite only for those of the true faith. After all, who has been a more eloquent spokesman for the common morality than Pope John Paul II? It is convenient for naysayers, consequently, to see the “common morality” as the surreptitious smuggling of dogma into the political debate.

Budziszewski comes back to this issue again and again, not least when he discusses Thomas Aquinas’s contention that the content of the Ten Commandments, with minor adjustments, is simply the common morality that everyone knows. The prohibitions against murder and lying and adultery are not binding only on those of the Old Convenant. Indeed, the Tables of the Law were given precisely because the behavior of the Jews had so long gone contrary to common morality that it was necessary that they be given a dramatic reminder on Mount Sinai. For Jew and Christian the divine sanction of the naturally knowable is a powerful reminder of what men can all too easily forget, their awareness eclipsed by misbehavior. The sanction is not what provides the primary grip of the prohibitions—however vulnerable to forgetfulness the non-religious, particularly, are.

If religious faith, the response to an authoritative revelation that is not simply the acceptance of what everybody knows, is not a substantive presupposition of the common morality, the question must arise as to whether the common morality reposes on acknowledgment of the existence of God. Here the reader may find Budziszewski somewhat ambiguous.

He makes a strong case for the dependence of any account of the common morality on God as the creator of the nature, whose mode of flourishing is written into that very nature. But this of course can be taken to mean only that the theory of natural law is inescapably based on theism, a contention with which I would agree. The more delicate question is whether any human agent need be explicitly aware of God’s existence in order to be guided by the common morality. Budziszewski seems to require this, and that is doubtless discussable.

A feature of natural law precepts, according to Thomas Aquinas, is that they are non-gainsayable, that is, self-evident. The only defense of them available is indirect, by convicting the one denying them of incoherence and inconsistency because he must invoke what he is in the process of denying. For Thomas, knowledge of God’s existence is not a self-evident truth. Indeed, philosophically, he locates it at the very end of a lengthy inquiry, its premisses reposing on a vast amount of previously established truths. It is this very difficulty of proving God’s existence that provides Thomas with one of his major arguments for the fittingness of Revelation.

In its discussion of atheism, the Vatican II document Gaudium et Spes makes the important point that denial of God is not the natural standpoint of the human mind. Nam atheismus, integre consideratus, non est quid originarium. This can only be true if there is some natural awareness of God’s existence. Budziszewski observes that philosophical proofs for the existence of God assume that talk about God is a familiar feature of ordinary human life. So there does seem to be pre-philosophical knowledge of God’s existence. But is it self-evident?

Jacques Maritain, in Approaches to God, devotes his opening chapter to this question and suggests, what seems obvious, that discourse and inference do not begin with formal philosophizing. One need not maintain that the existence of God is self-evident to all in order to say, as Maritain does, that there is an easy pre-philosophical inference from the world around us to the cause of it all. He calls this inference “virtually metaphysical.” Perhaps this is all Budziszewski needs to make his point.

Budziszewski confronts with relish what must seem to be the most obvious obstacle to his thesis. What is to be done with the many who would simply say that they do not know what Budziszewski says that everyone knows? We have here one of the most important contributions of this book. It is well known that when Thomas Aquinas introduces the first principles of practical reasoning—natural law—he shows what he means by invoking the first principles of all reasoning, the self-evident truths on which all discourse depends, such as, notably, the principle of non-contradiction. Despite this parallel, it has been the rare person who has undertaken to apply to the first practical principles the logical and rhetorical devices used to defend the theoretical first principles against attack. Budziszewski is that rare person.

Plato and Aristotle took very seriously the position of Protagoras according to which what is true for me is true for me and what is true for you is true for you. In their different ways, the two giants of Greek philosophy displayed the incoherence of the claim and its reliance for intelligibility on the very principle it would deny. That is the technique that Budziszewski applies to the denial of the fundamental truths of the common morality. But there are two moments in his treatment.

First, is the simply logical. Of course few of us enjoy being told that we are speaking incoherently and since Budziszewski is not interested in demolishing opponents so much as enabling them to see that they cannot really be opposed to the common morality, he introduces a second moment, one that could be called persuasive or rhetorical. Budziszewski after all is not out to gain adherence to his viewpoint, as if he owned it or as if his interlocutor could really occupy a different position. The response he is after is not capitulation to the Budziszewski theory but the inner recognition of anyone’s best lights, which may have been dimmed but cannot go completely out.

One of the difficulties any appeal to common sense must face is that a lot of nonsense is commonly believed. If the common morality meant merely a consensus of moral beliefs at any given time it would constantly fluctuate—and of course would involve a decision as to which beliefs count. On this level, the level of polling, let us say, it might seem very difficult to locate the common morality Budziszewski reminds us of. It is another merit of this book that this all too familiar difficulty is addressed effectively and at length.

The fact/value dichotomy? Budziszewski gives it the short shrift it deserves. All in all, this is an enormously important book, well-written, well-argued and, let it be said, well-designed and printed as well. Once more Budziszewski has put us in his debt. Odd as it may seem, any reader will learn a lot from What We Can’t Not Know.