Hume

David Hume

David Hume was, by every account, the most good-natured man in the history of philosophy, beloved in the salons of Paris and the taverns of Edinburgh, stout and cheerful and kind, nicknamed le bon David, the good David. He was also the most quietly devastating skeptic the West has ever produced. With unfailing politeness and irresistible clarity, Hume took the things every human being believes without question, that the sun will rise tomorrow, that one event causes another, that there is a real world out there, that you are a single continuous self, that some acts are truly right and others wrong, and showed, one by one, that none of them can be justified by reason. We cannot prove the future will resemble the past. We never actually observe causation. We cannot find the self when we go looking for it. We cannot squeeze a single "ought" out of any list of facts. It sounds like a recipe for despair, and in a colder man it might have been. But Hume drew the opposite conclusion, and it is the key to all his work: that since we manifestly do live by these beliefs, and could not survive a day without them, they must rest on something other than reason. They rest on habit, on feeling, on human nature itself. We are not the rational animals we flatter ourselves to be. We are creatures of custom and sentiment, who reason far less, and far later, than we like to think.

The missing connection. His most famous demolition concerns the idea we lean on more than any other: cause and effect. Watch one billiard ball strike another and send it rolling. You say the first ball caused the second to move, and you feel you have watched the causing happen. But look harder, Hume says, at what your senses actually delivered. You saw the first ball approach. You saw it touch. You saw the second ball move. What you did not see, ever, anywhere, was the connection between them, the supposed power or necessity by which the one makes the other move. You saw one thing, and then another thing; you never saw the "and therefore." All we ever observe in the world is one event followed by another, over and over, what Hume calls constant conjunction, never the hidden link the word "cause" promises. So where does our overwhelming sense of necessary connection come from? Not from the world, Hume answers, but from us. Once we have seen two things go together often enough, the mind forms a habit, so that when the first appears we automatically expect the second, and we then project that inner feeling of expectation out onto the world and call it a necessary connection in things. Causation, the very glue of the universe, turns out to be, in part, a habit of the human mind. It is one of the deepest and most disturbing results in all of philosophy. A Muslim theologian, al-Ghazali, had felt his way toward something similar seven centuries before; Hume gave it a rigor from which it has never recovered, and the problem he opened, of how, or whether, we can ever justify our trust in causes and in the regularity of nature, is genuinely unsolved to this day.

The self that isn't there. Hume turned the same searching method on the most intimate thing of all: your own self. Surely, whatever else is uncertain, you know that you exist, a single, continuous self, the "I" that has all your experiences. Hume asked a simple, terrible question: have you ever actually perceived this self? Look inward, he says, and try to catch it. What do you find? Always some particular experience, a warmth, a pang, a color, a thought, but never the bare "self" that supposedly has them all. "When I enter most intimately into what I call myself," he wrote, "I always stumble on some particular perception or other, and never can catch myself at any time without a perception." All you ever find, in other words, are the experiences; the "I" that owns them is nowhere among them. So perhaps, Hume suggests, there is no such thing, no unchanging soul or substance underneath, only a bundle of perceptions, a rapid, ceaselessly changing flow of sensations and feelings that we tie together with memory and call a self, the way a nation is nothing over and above its citizens, or a river nothing over and above the water passing through. It is a vertiginous thought, and a strikingly modern one: the very conclusion the Buddhist tradition had reached on the far side of the world, and one that neuroscience and the builders of artificial minds now circle again. The self may be less a thing than a process, less a noun than a verb.

Reason is the slave of the passions. If reason cannot ground our beliefs about the world, can it at least ground our morality? Here Hume delivered his most quoted and most misunderstood line: "Reason is, and ought only to be, the slave of the passions." He did not mean that we should be impulsive. He meant something precise and deep: that reason alone can never move you to act, and never by itself makes anything good or bad. Reason tells you what is, the facts, the means, the consequences; but it is silent on what matters. Only feeling, desire, sympathy, a sense of approval or revulsion, can make you care, and care is what drives every choice and grounds every value. He sharpened this into a famous logical observation that still haunts ethics: that you can never validly derive an "ought" from an "is," never squeeze a single value out of any quantity of pure facts, because the facts tell you how the world is and stay stubbornly silent on how it should be. Morality, then, is not a body of truths that reason discovers, like geometry; it is rooted in human sentiment, in our natural capacity to feel for one another, to be warmed by kindness and sickened by cruelty. This was scandalous in his day and is bracing still, but notice that it is not cynical: Hume believed our moral feelings, and especially sympathy, the power to feel what another feels, were real, deep, and largely benevolent. He took morality away from cold reason and handed it back to the warm, fellow-feeling creature that a human being actually is.

No designer in the evidence. Hume saved his most careful, and most dangerous, demolition for the Dialogues Concerning Natural Religion, a book he wrote with great care and was in no hurry to print. In it he took apart the most popular argument for God of his age, the argument from design, which reasons that the world is so intricate, so finely arranged, that it must have had an intelligent designer, as a watch implies a watchmaker. Hume, reasoning strictly from the evidence and nothing else, showed how little it will bear. The world is not really much like a watch; it resembles a growing plant or an animal at least as much as a machine, and from those you would infer no watchmaker at all. And even if you grant a designer, the evidence will not yield the God people want: from a finite world you can infer at most a finite cause; from a world so full of waste and suffering you cannot honestly infer a perfectly good one; you might as well conclude that this world was the bungled first attempt of some inferior deity, or the committee-work of several. The old question Cicero had staged among the Roman schools, whether the order of nature proves a divine mind, Hume pressed to its uncomfortable end: if you reason only from what you actually see, the evidence of the world simply does not deliver the good, infinite, personal God of religion. You may believe in such a God, Hume implies, but not because the world has proven him to you.

Be still a man. The room holds Hume's main works, the early Treatise that "fell dead-born from the press" and the polished Enquiries that made his name, plus theDialogues on religion that he prudently kept from the press; cite them by section. And it is worth being clear, at the end, about what kind of skeptic he was, because it is easy to get wrong. Hume did not think his arguments should make anyone miserable, or keep them from living. The cure for too much philosophy, he said cheerfully, is more life: when his skeptical reasonings grew oppressive, he would dine, play backgammon with his friends, and come back to find the doubts had lost their sting, not refuted, but simply outweighed by the irresistible force of nature and habit, which carry us through the day no matter what the philosophers prove. "Be a philosopher," he wrote, "but, amidst all your philosophy, be still a man." This mild, livable skepticism, doubt everything in the study, but trust nature, habit, and good company in the street, is one of the sanest postures any thinker has ever offered. Its influence has been immense. Hume jolted Kant out of what Kant called his "dogmatic slumber" and forced the whole next age of philosophy to reckon with the limits of reason; he founded the empirical study of the mind and of morals; and his quiet demonstration that we are feeling, habit-driven creatures who reason far less than we suppose has been confirmed, over and over, by the sciences of the mind that came after him. He set out to show us what reason cannot do, and ended by showing us, far more gently than we deserved, what we actually are.