David Hume was apparently excellent company, which is rather surprising when you consider how thoroughly he unsettled some of the most cherished assumptions of his age.
He was genial, sociable, fond of conversation and possessed of a healthy appetite. His friends found him affectionate and good-humoured. Yet this agreeable Scotsman devoted much of his intellectual life to questioning how we know what we think we know, whether reason governs our conduct, and how much confidence we can place in the explanations we construct about the world.
He was also sufficiently troublesome to the religious establishment that he never secured the university professorship he sought.
I imagine dinner with Hume would have been entertaining, provided you didn’t mind discovering, somewhere between the soup and the pudding, that your most firmly held convictions rested on rather shakier foundations than you had supposed.
An Edinburgh Education
Born in 1711, Hume grew up in a Scotland undergoing extraordinary intellectual change. Edinburgh was becoming a centre of argument, inquiry and sociability, where lawyers, physicians, philosophers and men of letters met to exchange ideas.
Hume attended the University of Edinburgh at an unusually young age, but his intellectual interests soon took him well beyond the conventional curriculum. He wanted to understand human nature, and he believed that the best place to begin was with observation.
This sounds unremarkable until we consider the intellectual climate in which he was working. Philosophers had long constructed elaborate accounts of knowledge, morality and human conduct, often beginning with principles they considered self-evident. Hume proposed examining how the human mind actually operates.
It was an ambitious undertaking. His first great work, A Treatise of Human Nature, appeared in three volumes in 1739 and 1740, when he was still in his twenties.
The reception was disappointing. Hume later joked that it had fallen “dead-born from the press.”
Fortunately, he did not conclude that the public’s failure to appreciate his genius required him to abandon the enterprise. He revised, reconsidered and presented his arguments in more accessible forms. His subsequent essays, philosophical enquiries and enormously successful History of England brought him the readership and reputation that the Treatise had failed to secure.
There is something rather appealing about a philosopher of intellectual humility who was obliged to practise a little of it himself.
Who Is Driving the Carriage?
We generally like to think of ourselves as reasonable creatures. We consider the evidence, weigh the alternatives and arrive at a decision. Emotion may occasionally interfere, but reason is supposed to be in charge.
Hume was unconvinced.
His famous declaration that “Reason is, and ought only to be the slave of the passions” sounds almost scandalous. Surely reason ought to govern our impulses rather than submit to them?
But Hume was making a more precise distinction. Reason helps us establish facts, understand relationships and calculate consequences. It can tell us that one course of action is likely to be more effective than another. What it cannot do, by itself, is supply the desire that makes us act.
A person may understand perfectly well that a particular investment is risky, a journey exhausting or an argument unlikely to end happily. Whether that understanding changes the decision depends partly on what the person values, fears or hopes to achieve.
Reason can advise the driver. It does not necessarily choose the destination.
This is not quite the same as saying that people make decisions emotionally and invent rational explanations afterward, although that certainly happens. Hume’s point was that human motivation cannot be understood by treating feeling as an unfortunate defect in an otherwise rational machine.
Our affections, ambitions, loyalties and aversions are not incidental to human conduct. They are among its driving forces.
The Trouble with Tomorrow
Hume’s examination of habit is, to my mind, even more unsettling.
Suppose we have observed the same sequence of events hundreds of times. One thing happens, and another follows. We come to expect that the relationship will continue. We may even conclude that the first event causes the second.
But those are different claims. We have observed a sequence, formed an expectation, and arrived at an explanation. Each step takes us further than the observation itself.
That expectation is indispensable to ordinary life. We plant crops, build bridges, make investments and arrange journeys on the assumption that the physical world will behave tomorrow much as it did yesterday.
But how do we know that it will?
We can point to all the occasions on which our expectations have been confirmed. Yet that argument assumes precisely what we are trying to establish: that past experience is a reliable guide to future events.
We are no less inclined to jump to conclusions when interpreting other people’s behaviour. A friend fails to return a telephone call. We wonder whether we’ve offended them. By the end of the afternoon, we’re quite convinced they’re angry with us. Yet all we actually know is that the telephone hasn’t rung.
Hume did not suggest that we should abandon experience or refuse to make predictions. Such a life would be impossible. Instead, he argued that our confidence arises from custom or habit. Repeated experience creates an expectation so powerful that we often mistake it for logical certainty.
Hume was not attacking science; he was examining the reasoning on which our knowledge of the world depends. His challenge is not to stop drawing conclusions, but to recognize how much—and how little—our observations actually establish.
A Skeptic in Good Company
You might think such arguments would have produced a rather gloomy character, but Hume was nothing of the sort.
He enjoyed society, cultivated friendships and participated enthusiastically in Edinburgh’s intellectual life. In 1754, he joined Adam Smith and the portrait painter Allan Ramsay in founding the Select Society, a debating club that brought together some of Scotland’s most accomplished thinkers.
Hume and Smith developed a particularly close friendship. They shared an interest in moral philosophy, commerce, human behaviour and the institutions through which people manage to live together.
Their approaches were complementary without being identical. Hume examined the foundations of knowledge, the origins of moral judgment and the conventions that sustain society. Smith explored sympathy, moral approval, specialization, exchange and the extraordinary coordination possible among people pursuing different purposes.
Neither man required human beings to be perfectly rational before attempting to understand how societies function. And neither seems to have believed that intellectual disagreement precluded affection.
Hume’s religious skepticism, however, had consequences. Opposition to his views helped frustrate his attempts to obtain university appointments. His arguments concerning miracles, religious belief and the limits of human knowledge were regarded by many contemporaries as deeply threatening.
That he nevertheless became a celebrated historian and philosopher says something about the intellectual energy of eighteenth-century Scotland. Its institutions could be resistant to unsettling ideas, even as its clubs, publishers and circles of friendship provided opportunities for those ideas to flourish.
Enter Rousseau
Hume’s friendship with Jean-Jacques Rousseau provides an almost irresistible episode in a life devoted to understanding human nature.
Rousseau, the celebrated and controversial philosopher, had fallen into difficulties on the Continent. Hume offered assistance, helped arrange his journey to Britain in 1766 and worked to secure him a place of refuge. The arrangement did not end well.
Rousseau became convinced that Hume was conspiring against him. What had begun as an act of generosity descended into accusations, correspondence and a very public quarrel.
For a philosopher who had spent years examining the influence of passion, suspicion and belief on human judgment, the experience must have been exasperating.
There is an additional irony. Allan Ramsay painted portraits of both men, and the pictures eventually hung together in Hume’s Edinburgh parlour, long after their relationship had deteriorated. I would dearly love to know what Hume thought when he looked at them.
It’s tempting to present the affair as a tidy demonstration of Hume’s philosophy: the reasonable skeptic confronted by a man overwhelmed by suspicion. But that would be too convenient. We know the dispute largely through accounts shaped by the participants and their supporters, and Hume himself was not immune to wounded pride.
Perhaps the more useful observation is that understanding human nature does not exempt anyone from its complications.
The Limits of Certainty
Hume’s skepticism is sometimes mistaken for a refusal to believe anything. In practice, he recognized that human beings cannot function without expectations, judgments and conventions.
We rely on experience because we must. We trust other people, though they sometimes disappoint us. We form explanations, knowing that additional evidence may require us to revise them. The danger lies less in having convictions than in forgetting the distinction between conviction and proof.
This was one of Hume’s most consequential contributions. He made it difficult to claim absolute certainty about matters grounded in experience, while leaving ample room for practical judgment. It is a demanding position. It asks us to reason carefully without imagining that careful reasoning makes us infallible.
And it leaves us with a philosopher whose life was rather more cheerful than his reputation might suggest.
A Most Human Philosopher
Hume died in Edinburgh in 1776, the year his friend Adam Smith published The Wealth of Nations. During his final illness, Hume remained remarkably cheerful, receiving visitors, enjoying conversation and displaying the good humour for which he was so widely loved.
Smith subsequently wrote a moving account of his friend’s final days, concluding that he had regarded Hume as approaching “as nearly to the idea of a perfectly wise and virtuous man, as perhaps the nature of human frailty will permit.”
It was an extraordinary tribute, particularly to a man whose religious skepticism had made him so controversial.
And perhaps that is where we should leave David Hume: not with another summary of his philosophy, but with the affection of someone who knew him well.
