Smith begins his discussion of David Hume’s moral and social philosophy.

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.

I wish to begin my discussion of the Scottish philosopher David Hume (1711–1776) with some inside baseball. By this I mean how Hume is sometimes viewed by those modern libertarians who have been influenced by Ayn Rand. Rand ranked Hume high on her list of intellectual villains, as we see in this passage from For the New Intellectual:

When Hume declared that he saw objects moving about, but never saw such a thing as “causality”—it was the voice of Attila that men were hearing. It was Attila’s soul that spoke when Hume declared that he experienced a flow of fleeting states inside his skull such as sensations, feelings or memories, but had never caught the experience of such a thing as consciousness or self. When Hume declared that the apparent existence of an object did not guarantee that it would not vanish spontaneously next moment, and the sunrise of today did not prove that the sun would rise tomorrow; when he declared that philosophical speculation was a game, like chess or hunting, of no significance whatever to the practical course of human existence, since reason proved that existence was unintelligible and only the ignorant maintained the illusion of knowledge—all of this accompanied by vehement opposition to the mysticism of the Witch Doctor and by protestations of loyalty to reason and science—what men were hearing was the manifesto of a philosophical move that can be designated only as Attila‐​ism.

Although I would not associate Hume’s epistemology with Rand’s literary ideal type of “Attila,” and though I might disagree with Rand’s characterization in other respects, I share her low estimation of Hume’s theory of knowledge, which I regard as quite crude —as when Hume treats ideas as nothing more than “faint images” of “impressions” (i.e., perceptions). Although Hume’s theory is sometimes represented as a continuation of Lockean empiricism, Locke’s careful analysis of abstractions in An Essay Concerning Human Understanding (1690), which resembles Rand’s approach in some respects, is far superior to anything found in Hume.

For Rand, a theory of knowledge is the sine qua non of a philosophy, the foundation that will profoundly affect one’s theory of ethics, politics, and so forth. Consequently, those libertarians who accept Rand’s approach tend to dismiss Hume out of hand, as if nothing he wrote could be of value. But, as many commentators have noted, there is a curious disconnect between Hume’s epistemological skepticism and his moral and social philosophy. As Charles W. Hendel explained in his Introduction (1957) to Hume’s An Inquiry Concerning the Principles of Morals (1752), “Hume was not skeptical in this work of moral philosophy.”

The first thing Hume insists upon against any skepticism in morality is “the reality of moral distinctions.” They are real and they are important. They are not merely matters of convention or products of education. They originate naturally in the life of man in society.

Of the book referred to by Hendel, An Inquiry Concerning the Principles of Morals (which would become the second part of Enquiries Concerning Human Understanding and Concerning the Principles of Morals), Hume later said that it was “of all my writings, historical, philosophical, or literary, incomparably my best.” Scholars disagree over whether the later Inquiry is merely a briefer and more elegantly written version of Hume’s earlier treatment of ethics in Book III of A Treatise of Human Nature (1739), or whether Hume changed his views somewhat in the later book. A Treatise of Human Nature, which is widely regarded as Hume’s true masterpiece, was written while Hume was a young man and unknown in literary circles. After it “fell dead‐​born from the press” Hume resolved to write a more accessible version of the ideas contained in A Treatise of Human Nature, which can be quite difficult to read, and this led to his shorter Enquiries, an exemplar of how to write philosophy in an essay style.

One thing is certain: In his later book on ethics Hume avoided some of the controversial language and expressions that appear in the Treatise. For example, we find no references in the Inquiry to justice being an artificial virtue—an unfortunate choice of words in the Treatise that generated considerable misunderstanding among readers (for reasons I will explain presently). Moreover, some of Hume’s hopped‐​up expressions in the Treatise do not appear in the Inquiry, most notably the infamous remark, “Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them.” One can imagine a young Hume being delighted with this striking bit of rhetoric, even though it could (and did) lead to misunderstandings about the points he wished to make in the Treatise. Hume was not the only young writer in the history of philosophy who was occasionally overexuberant.

F.A. Hayek was the chief conduit through which Hume’s moral, political, and social theory entered the mainstream of modern libertarian thought. In his article “The Legal and Political Philosophy of David Hume” (originally presented as a lecture at the University of Freiburg on July 18, 1963), Hayek bemoaned the fact that Hume’s legal and political philosophy had been “curiously neglected.” In addition to being “one of the founders of economic theory” and the greatest British legal philosopher before Bentham, Hume “gives us probably the only comprehensive statement of the legal and political philosophy which later became known as [classical] liberalism.” Although I think Hayek sometimes cast Hume’s ideas in a more favorable light than they warrant, his article remains essential reading for libertarians who want to understand Hume’s contributions to classical liberalism.

In this essay (and the one to follow), I can do no more than sketch some of Hume’s ideas in moral and social philosophy, especially as they pertain to self‐​interest, social order, and utility. First, however, I wish to clear up a controversy that I mentioned previously, namely, Hume’s references, in A Treatise of Human Nature, to justice being an “artificial” virtue, or an “invention” (as he sometimes called it).

This language, which Hume later abandoned, provoked a good deal of criticism from his contemporaries, who claimed that Hume was attempting to overthrow a natural‐​law ethics in favor of moral subjectivism. But even in the Treatise Hume made it clear that he had no such intention. (For an excellent discussion of this problem, see Stephen Buckle, Natural Law and the Theory of Property: Grotius to Hume, Oxford University Press, 1991.) As Hume wrote in A Treatise of Human Nature:

To avoid giving offense, I must here observe, that when I deny justice to be a natural virtue, I make use of the word natural, only as opposed to artificial. In another sense of the word; as no principle of the human mind is more natural than a sense of virtue; so no virtue is more natural than justice. Mankind is an inventive species; and where an invention is obvious and absolutely necessary, it may as properly be said to be natural as any thing that proceeds immediately from original principles, without the intervention of thought or reflection. Though the rules of justice be artificial, they are not arbitrary. Nor is the expression improper to call them Laws of Nature; if by natural we understand what is common to any species, or even if we confine it to mean what is inseparable from the species.

Justice, according to Hume, is not a natural sentiment of human beings (such as the affection that a mother feels for her child), nor is it an eternal truth discernible by reason alone, independently of experience. Rather, justice is a social phenomenon, one that emerges over time as people reflect on how they benefit from social interaction and how those benefits can be preserved.

To say that the rules of justice are not arbitrary is to say that they cannot be altered or abolished by human will or decree—a crucial tenet of the natural‐​law tradition. People come to value justice as essential to society because it is in fact essential to society. We come to formulate the rules of justice after sufficient experience and reflection teach us their role in preserving social order. Thus, in referring to the rules of justice as “conventions,” Hume meant that they must be discovered over time, through the trial and error of circumstances, as experience reveals their usefulness, or utility. The rules of justice cannot be deduced from axiomatic premises by reason alone; they depend on experience and on our analysis of that experience, which teach us the indispensable role that justice plays in maintaining social order.

In order to appreciate what Hume was getting at, we need to know something about the tradition he opposed. There were two broad currents in British moral philosophy during the eighteenth century: One, as I explained in the first essay of this series, is “sentimentalism”—so called because of its focus on the role played by human sentiments (feelings, emotions, etc.) in human action, a role that must be appreciated if we are to understand why humans behave as they do and how social cooperation comes about. The second current is commonly called “moral rationalism”—so-called because of its claim that justice and other moral principles can be derived and justified by reason alone.

Moral rationalism was the target of Hume’s critical analysis of reason in moral philosophy, and of his celebrated Is‐​Ought dichotomy. Moral rationalists, said Hume, defend “an abstract theory of morals” and pretend “to found everything on reason,” while ignoring the role of sentiments and passions in the evolution of institutions, such as property. According to moral rationalism, our notions of virtue and vice, right and wrong, justice and injustice, have their origin in reason alone, in the same way that our scientific and mathematical notions originate in reason. Our practical knowledge of ethics, like the theoretical knowledge of mathematics, can be logically demonstrated, according to rationalists; both are based on the “eternal and unalterable relations” of their respective subject matters. Moral obligation, in this view, is a species of rational obligation. Just as we are constrained to accept mathematical propositions when their truth becomes evident to the mind, so we are similarly constrained to accept ethical prescriptions.

The approach to which Hume objected is found in the writings of Samuel Clarke, a well‐​known philosopher and theologian of the time. (Another rationalist was William Wollaston, an influential eighteenth‐​century philosopher specifically mentioned by Hume.) According to Clarke (Discourse Upon Natural Religion, 1706), there is a Rule of Equity which states that “we so deal with every Man, as in like Circumstances, we could reasonably expect he should deal with Us….” The human understanding naturally submits to a demonstrated truth. It is not a matter of will, for example, whether we believe that twice two equals four. Once we clearly understand what numbers mean and how they are related mathematically, we have no choice but to accept the proposition “2 + 2 = 4” as necessarily true. Similarly, once we understand the nature of human beings and their social relationships, we have no choice but to accept the truth of basic moral propositions, such as the Rule of Equity. Quoting Clarke:

For, as the addition of certain numbers, necessarily produces a certain sum…so in moral matters, there are certain necessary and unalterable respects or relations of things, which have not their original from arbitrary and positive constitution, but are of eternal necessity in their own nature.

The following argument by Clarke was typical of moral rationalists.

The reason which obliges every man in practice, so to deal always with another, as he would reasonably expect that others should in like circumstances deal with him, is the very same, as that which forces him in speculation affirm, that if one line or number be equal to another, that other is reciprocally equal to it. Iniquity is the very same in action, as falsity or contradiction in theory, and the same cause which makes one absurd, makes the other unreasonable. Whatever relation or proportion one man in any case bears to another, the same that other, when put in like circumstances, bears to him. Whatever I judge reasonable or unreasonable for another to do for me, that, by the same judgment, I declare reasonable or unreasonable, that I in the like case should do for him. And to deny this in either word or action, is as if a man should contend, that, though two and three are equal to five, yet five are not equal to two and three.

It was in reaction to his kind of hyper‐​rationalism that the sentimentalists, such as Shaftesbury, Hume and Adam Smith, proposed an alternate psychological and sociological theory of justice, one that took into account the role of human passions in the genesis of moral principles and social institutions, such as private property. I will examine this approach, as developed by Hume, in my next essay.