Recently recognized was the three-hundredth anniversary of the birth of the Scottish philosopher David Hume. Celebrations were international but focused especially on his native Edinburgh, where the university has been keen both to honor his presence as a student there, and to make recompense for the fact that in 1745 it rejected his application for a professorship in philosophy—as, in 1751, did Glasgow University, preferring to appoint Adam Smith. Ironically, Smith based his own theory of ethics on Hume’s ideas, and they became close friends, with Hume naming Smith to be his literary executor.

Today Hume is recognized as a philosophical genius and widely held to be the greatest philosopher in the English language. Yet the unfavorable verdict of many of his contemporaries is intelligible, and not only for the reason celebrated by his current admirers, namely that he was hostile to religious belief and practice. For Hume advanced a philosophy that, if taken at face value, would not only undermine the claims to truth of religion but those of morality and of science also.

He also favored Toryism against Whiggism in politics and in history, and urged the cause of economic freedom as a precondition of political liberty. One might be puzzled at how a philosophical radical regarding traditional beliefs could incline to conservative ideas with respects to practices and institutions, but there is no great mystery. The latter is a response to the former, as we will see.

Hume believed that the power of reason is largely negative, showing that seemingly settled beliefs rest on shallow and insubstantial foundations. Not only are familiar intellectual convictions ungrounded but they must remain forever so, since secure knowledge is an impossibility. Hence, while his religious “impiety” counted against him, so too did his general skepticism.

Hume was fully aware of the revolutionary nature of his conclusions, and of the originality of the arguments by which he reached them. He wanted to be recognized nationally and internationally and was disappointed at the limited appreciation he received in his own lifetime. But he was also possessed of great ease and amiability and never became bitter, rancorous, or self-pitying. In later life he served for three years as acting secretary to the British embassy in Paris, where he much enjoyed literary society and was himself greatly appreciated, earning the sobriquet “le bon David.” The combination of high ambition and deep contentment is rare, and it exposed failings in the understanding of even his most sensible, and sensitive, contemporaries.

In his Life of Samuel Johnson, Boswell records telling the good Doctor that Hume’s “persisting in his infidelity, when he was dying, shocked me much.” Johnson replied that Hume “had a vanity in being thought easy. It is more probable that he should assume an appearance of ease, than that so very improbable a thing should be, as a man not afraid of going . . . into an unknown state.”

This was uncharacteristically misjudged. Johnson was a sincere moralist and a devout Anglican and could give no more credit to Hume’s rejection of the reality of values and of God and the soul than he could to Bishop Berkeley’s denial of the reality of matter. When Boswell had said that, absurd as Berkeley’s philosophy might be, it was impossible to refute it, Johnson responded by “striking his foot with mighty force against a large stone, till he rebounded from it, saying, ‘I refute it thus.’”

Just as that misses the point of Berkeley’s metaphysics, so his refusal to take seriously Hume’s deathbed ease in unbelief says more about his lack of a philosophical temperament than about the authenticity of Hume’s belief. The question is not whether he was sincere in his beliefs but rather what they were and whether they are compelling.

Hume was a prodigy and published his system of philosophy while in his mid-twenties in the form of A Treatise of Human Nature. He had entered university at the age of twelve but quickly discovered that he would learn more from private reading, later telling a friend that “there is nothing to be learnt from a Professor, which is not to be met with in Books.”

It was also early on that he conceived what he termed “a new Scene of Thought,” and he then set about systematically reading in order to present his own new philosophy in a way that took note of the ideas of the past and present. That process took a decade and led him to live abroad using the library of the Jesuit college in La Flèche, where Descartes had been a student a century before.

Ever the ironist, Hume must have delighted in the incongruities. The Jesuits had been founded by Ignatius Loyola to serve the pope in countering the intellectual forces of the Protestant Reformation, and Descartes had set himself the task of establishing with certainty the existence of God, the soul, and the world. Having rejected religious belief, Hume retained the fervent anti-popery of his Calvinist formation, and now he was setting about fashioning a philosophy that would pull apart the very structure that Descartes had so carefully assembled.

Was Hume, some wonder, too quick, spurred on by genius and ambition but failing to register what a slower and more mature mind might have noticed and reflected upon? Hume seems himself to have recognized that his desire for reputation and literary fame may have led him to rush into print. In “My Own Life,” a short autobiography composed shortly before he died, he wrote: “I had always entertained a notion, that my want of success in publishing the Treatise of Human Nature, had proceeded more from the manner than the matter, and that I had been guilty of a very usual indiscretion, in going to the press too early.”

Hume’s main distinction lay in two contributions. First, in carrying through the implications of his idea that all knowledge resides in experience; and second, in providing an alternative account of the source and persistence of our beliefs. The claim that knowledge derives from experience was not new. Locke got it from the medieval scholastics, who got it from Aristotle. But when the scholastics wrote “nihil est in intellectu quod non prius in sensu”—there is nothing in the mind that was not first in the senses”they did not mean to confine knowledge to what is immediately sensed: odors, tastes, colors, sounds. Rather, they took these “qualities” (“impressions” in Hume’s terminology) to comprise the media through which reality is discerned and understood. One only knows about cats and dogs through sensations, but they are not themselves sensations, any more than the players in a televised football game are color patterns on a flat screen.

In Hume’s “new Scene,” however, we are confined to sensations and their psychological effects, and all claims to knowledge of an external world of natural objects and their causes are groundless, as are claims to intuit or infer the existence of the soul and of God. Likewise, morality dissolves into impressions and sentiments. Had this been where Hume’s philosophy ended, subsequent generations might have dismissed it, as did his contemporaries, who viewed his radical skepticism as absurd and dangerous.

This, however, neglects his second and more constructive contribution. It involves an approach then barely conceived of, namely the psychology of human thought and behavior. What he took away by denying the possible objectivity and rationality of belief, he returned by reconceiving common sense and common action as expressions of natural inclinations and habits. We think there is a world around us not because we really see it or reliably deduce it but because we are naturally inclined to think in this way. We applaud benevolence and abhor cruelty not because we recognize objective good and evil but because we are naturally possessed of certain sentiments that express themselves in approval and disapproval.

Traditional philosophy dealt in the currency of truth and reason; Hume replaced these with the commodities of sentiment and habit. He was right, therefore, to judge that he was offering something new to the world.

Here lies the explanation for the way in which Hume combined his philosophical radicalism with his political Toryism. His skepticism undermines the idea of objective truth and thereby gives reason to be suspicious of claims and policies based on the assumption of it. His psychologism reorients the search for guidance away from reason toward human nature itself and therefore favors widely distributed and long-established practices over novel schemes of improvement. Precisely because sure knowledge is unavailable, it is fruitless to go in search of it and dangerous to imagine that we are progressing on the basis of it.

We can agree with Hume’s prudent opposition to progressivism and to abstract ideology without agreeing to his skeptical philosophy. He was certainly right to see the importance of human psychology, but just as he raced too quickly from the truth that knowledge rests on sensation to the conclusion that it is confined to it, so he assumed that we can only inhabit our psychology and not evaluate it.

Had he been in less of a hurry to astound the world with his new philosophy, he might have taken the time to read more widely in the library at La Flèche. Had he done so, particularly attending to works of patristic and medieval thought, to which by training, time, and temperament he was ill disposed, he might have encountered ideas that would have given him cause to think again. Long before his birth, authors such as Thomas Aquinas and Augustine had speculated about the nature of perception and knowledge, entertaining and then rejecting views similar to his theory of impressions.

Similarly, they had considered and endorsed the idea that sentiments (“passions”) and other aspects of human psychology are central to understanding and to morality; but they then went on to ask about the relation between what we feel and fear or hope for, and the nature of reality itself. Hume excluded the possibility of asking this by denying that we can have access to reality, and in that way reduced philosophy to psychology.

His Scottish contemporaries might not have put it that way, and insecurity may have blinded them to seeing his genius and his sincerity, but even so, they weren’t altogether wrong in thinking there was something dubious and even destructive in the thought of David Hume.

John Haldane is professor of philosophy at the University of St. Andrews.

Articles by John Haldane