David Hume: Skepticism, Empiricism, and the Limits of Reason

The most quoted deathbed scene in the history of philosophy is the one in which David Hume, asked by his friend James Boswell whether he did not now feel some uneasiness about having “left no behind him any one who might be willing to defend his philosophical opinions,” replied that he was “in the most whimsical situation imaginable.” Boswell, in the Life of Johnson, treats the remark as a piece of impenitence. It was, in fact, something more interesting: the last public statement of a philosopher who had spent forty years arguing that the deathbed is a very bad place to be making philosophical decisions, and that the proper time to settle the question of the immortality of the soul is before one is in a position to be carried off by it.

Hume was the most formidable skeptical philosopher of the Enlightenment, the most important British philosopher of the eighteenth century, and the writer whose work — by his own private estimate, expressed in the posthumously published Dialogues Concerning Natural Religion — most needed to be published posthumously. He knew what he was doing. He did it anyway, and the two facts together are part of the explanation for why his work has been, since the 1740s, the indispensable starting point for any serious engagement with the British philosophical tradition.

The Life

Hume was born in Edinburgh on May 7, 1711, the younger of two sons of a moderately well-off family of the Scottish gentry. His father died when he was two, and he was brought up by his mother, Katherine Falconer, who, by all accounts, was a remarkable woman — pious, well-read, and possessed of a kind of practical shrewdness that her famous son, who had less of it, would occasionally go to her for. The young Hume was supposed to study law. He studied, instead, the philosophical literature that was available in the Edinburgh of the 1720s — Locke, Berkeley, Malebranche, the Encyclopédie of Chambers — and decided, before he was twenty, that the philosophical tradition of the seventeenth century was, in important respects, incoherent. The decision was the great fact of his life.

In 1734, after a serious illness that he interpreted as a near-death experience, he resolved to devote his life to the development of a “new science of human nature,” modeled on the experimental philosophy of Newton, that would apply the methods of the natural sciences to the phenomena of the mind. The result was the Treatise of Human Nature, published in 1739–1740, when Hume was twenty-eight. The book sold fewer than a hundred copies in the first year, and Hume’s own summary of the reception — “it fell dead-born from the press” — is more accurate than the usual Enlightenment hagiography allows. The book was not, in fact, ignored. It was read carefully by some of the best minds in Britain and France, and most of them were scandalized. The two most important early readers were the clergyman William Law (author of A Serious Call to a Devout and Holy Life) and the philosopher-polemicist James Butler, the future Bishop of Durham, whose brilliant but somewhat unfair Analogy of Religion (1736) had been read by Hume and is in part an answer to the Treatise’s skeptical arguments about causation.

The next decade and a half was a long, slow recovery. Hume rewrote the first book of the Treatise as the Enquiry Concerning Human Understanding (1748), the third book as the Enquiry Concerning the Principles of Morals (1751), and published the two Enquiries, the Essays, Moral, Political, and Literary (1741–1742, expanded in many later editions), and the Political Discourses (1752). The Enquiries did better than the Treatise, but the real audience for the Enquiry Concerning Human Understanding was small, mostly English clergymen and university tutors, and the book’s reputation as the central text of British empiricism was established only in the nineteenth century.

The most charming period of his life was the Paris embassy, 1763–1766. Hume was secretary to the Earl of Hertford, the British ambassador, and he spent three years as the most famous Scotsman in France, feted by the philosophes, elected to the Académie des Sciences, and mildly embarrassed by the volume of attention. He met Rousseau, in a friendship that has been the subject of more biographical ink than any other in the history of the French Enlightenment, and that ended, in 1766, in a quarrel that is one of the longest-running scandals in the history of European letters.

The last decade of his life, in Edinburgh, was the period of the Dialogues Concerning Natural Religion (composed 1751–1776, published posthumously in 1779) and the History of England (1754–1762, in six volumes, ending with the Glorious Revolution). The History was the best-selling of all his works in his lifetime — it went through more than fifty editions in fifty years — and the Dialogues was the one he was most careful to keep out of print. He instructed his executors, Adam Smith and the Edinburgh lawyer Alexander Wedderburn, to publish it three years after his death. Smith and Wedderburn, after some hesitation, did so, and the Dialogues has been the most-read of Hume’s works in every generation since.

The Skeptical Argument

The Treatise of Human Nature is, by general agreement, the most ambitious work of philosophy written in the English language between Locke and Wittgenstein, and one of the three or four most ambitious works of modern philosophy in any language. The book is divided into three parts — “Of the Understanding,” “Of the Passions,” “Of Morals” — and the work as a whole is an attempt to apply the experimental method of natural science to the three great topics of the philosophical tradition: knowledge, action, and value.

The most famous argument is the analysis of causation in the first book. We believe, Hume argues, that one event causes another on the basis of “constant conjunction” — the observation that A has always been followed by B — and “habitual association” — the mental disposition, produced by that observation, to expect A to be followed by B in the future. But the expectation, Hume argues, is not based on any rational insight into a necessary connection between A and B. There is no logical contradiction in supposing that A might not be followed by B tomorrow. The necessary connection is a feeling, not a perception. The conclusion is that causation, in the strict sense in which the word was being used by Locke and by the scientists, does not exist. There are only constant conjunctions and the expectations they produce.

The argument was, in the eighteenth century, as unsettling to the physicists as it was to the theologians. Newton’s law of universal gravitation was, on Hume’s account, not a description of a real connection in nature but a habit of mind produced by the observation of falling apples. The argument is, in fact, more devastating to the physicists than to the theologians, and Hume was careful, in the Enquiry Concerning Human Understanding, to insist that the skeptical argument does not, in practice, “infect” the sciences. Nature, as he famously put it in Section XII, is “forceful” against skeptical arguments. We cannot give up our habits of causal reasoning, even when we recognize that they are not grounded in rational insight. We dither about the foundations of induction, and then we go and play backgammon.

The conclusion is often read as a kind of quietism — Hume as the witty skeptic who entertained himself and his readers with paradoxes and then sent them out into the world to be deceived. The reading is wrong. The argument is a serious critique of the pretensions of rational theology and rational metaphysics, and the proper response to it, in Hume’s view, is not to give up the sciences but to give up the claim that the sciences have a rational foundation in the strong sense that the seventeenth century wanted them to have. The right epistemic attitude is, in Hume’s account, a kind of modest knowing — the recognition that we can have no more certainty about the connection of causes and effects than the regularities of past experience can give us, and that this is, on the whole, enough.

The Passions and the Self

The second book of the Treatise develops a theory of the passions that is in some ways the most original part of Hume’s philosophy. The standard rationalist account of motivation — descended from Plato and Aristotle, and still dominant in the schools — held that the passions are subordinate to reason, and that reason can train, direct, or even overrule them. Hume’s argument is that the rationalist account reverses the relationship. The passions are the original springs of all human action. Reason is the slave of the passions, in the famous phrase of the Treatise (2.3.3), and serves the ends that the passions set. The role of reason is not to set ends but to discover the causal connections that allow us to pursue the ends we already have. Reason is, in a phrase Hume uses, “the slave of the passions, and can pretend to no other office than to serve and obey them.”

The argument was the basis of Hume’s most famous intervention in the philosophy of mind, the bundle theory of personal identity. The standard view, going back to Locke, was that the self is a substance — a thing that persists through time and is the subject of mental states. Hume’s argument is that, when we look for the self, we find only a “bundle” of perceptions — sensations, memories, desires, beliefs — connected by resemblance and causation, but not by any underlying substance. The conclusion was, in the eighteenth century, deeply shocking. Kant, who read the Treatise as a young man, reported that it interrupted his dogmatic slumbers. The shock was not that the self was illusory. The shock was that the argument seemed impossible to refute.

Morality and the Foundations of Sympathy

The third book of the Treatise is the most under-read part of the book and, in the judgment of the most recent scholarship, the most important. Hume argues that moral distinctions are not derived from reason (as the rationalist tradition had claimed) and not from self-interest (as Hobbes and Mandeville had claimed). They are derived from a moral sentiment — a feeling of approval or disapproval that human beings naturally experience when they observe actions that are useful or harmful to others. The sentiment is grounded in sympathy, the natural human capacity to share in the feelings of others, and it operates through a complex set of psychological mechanisms that Hume describes with great care.

The argument is one of the most influential in the history of moral philosophy. It was the basis of the Scottish moral philosophy of the late eighteenth century, of Adam Smith’s Theory of Moral Sentiments, of the moral-sense tradition in Britain, and (with various modifications) of the moral sentimentalism that has been the dominant tradition in English-language moral philosophy since the 1990s.

The scholarly debate about whether Hume was, in the strict sense, a moral sentimentalist has gone on for two hundred years. The older view — most influentially argued by Norman Kemp Smith in The Philosophy of David Hume (1941) — was that Hume’s moral theory is a “rational intuitionism” that depends, in the end, on a non-inferential intuition of moral truths. The more recent view, in the work of Rachel Cohon, of Terence Penelhum, of the late James King, and of the Scottish moralists themselves, has been that the moral sentimentalism is, in fact, Hume’s central doctrine, and that the rationalist readings underestimate the scope of the sentiment-based theory. The argument is well advanced, but it is not yet closed.

The History and the Dialogues

The History of England (1754–1762) is one of the most influential works of historical writing in the English language. It was the first comprehensive history of England to take the methods of the new critical historiography seriously, and it set the standard for the kind of political narrative that would dominate the writing of English history in the nineteenth century. The famous “Digression” on the early parliaments is one of the founding texts of the modern historiography of English constitutionalism. The history was controversial in its time — it was attacked by both Whigs and Tories for its apparent impartiality — but it was the standard account for the better part of a century and a half.

The Dialogues Concerning Natural Religion is one of the great works of philosophical theology. The dialogue is between three characters: Cleanthes, who defends the argument from design; Demea, who defends a more austere, mystical theology; and Philo, the skeptical critic of both. The work is a sustained and brilliant critique of the classical arguments for the existence of God, and the position of the author — identified in the private correspondence with Philo, but not in the text — is, in fact, more careful than the simpler readings of Philo’s position suggest. Hume is not, in the Dialogues, an atheist. He is a philosopher who has concluded that the natural-theology arguments, on which the moderate Enlightenment had relied, do not work, and that the proper response to their failure is a kind of reverent agnosticism.

A Judgement

Hume is, in the judgment of this writer, the most underrated of the great Enlightenment philosophers. The reason is partly that his conclusions are uncomfortable for modern readers — the rejection of the rationalist theory of the will, the bundle theory of personal identity, the skepticism about natural theology. The reason is partly that he is, in the conventional rankings, eclipsed by Kant, who took the Humean critique as the starting point for his own philosophy. The reason is partly that the Treatise is a long, badly written, and in places frankly dull book, and that the Enquiries, which are better, do not, in themselves, give a fair sense of the philosophical ambition of the project.

The contemporary revival of Hume scholarship — the work of Simon Blackburn, of Don Garrett, of James Harris, of the late John Passmore — has done much to restore the Treatise to the central place in the philosophical curriculum that the Enquiry has long occupied. The verdict that comes out of this body of work is that the Treatise is, in fact, the more important of the two books, and that the skeptical arguments of the Enquiry — the famous section X on miracles, the famous section XII on the limits of reason — are best read as a précis of the longer argument of the Treatise. The Treatise is the book that Hume wrote, the Enquiry is the book that he thought the world was ready for. The world, two hundred and fifty years later, is just beginning to be ready for the Treatise.

The Humean lesson, for the modern reader, is the importance of intellectual humility. The right epistemic attitude is not the strong rationalism of the seventeenth century — the belief that the mind can achieve certainty about the fundamental structure of the world — nor the strong empiricism of the nineteenth century — the belief that science can give us a complete description of reality. It is the modest recognition that human reason has real but limited powers, and that the proper role of philosophy is to identify the scope and the limits of these powers, not to construct grand systems that go beyond them. This was a lesson that the Enlightenment had difficulty learning. It remains a central challenge of contemporary philosophy.