Hume's Enquiry Concerning the Principles of Morals: The Anatomy of Human GoodnessLink Copied

Why do you recoil when you see someone kick a dog? Not because you've reasoned your way to a conclusion about animal welfare. The reaction is immediate, visceral, largely involuntary. Something in you responds before your rational mind has a chance to weigh in.

This observation, so obvious once stated, upended centuries of moral philosophy. David Hume argued that our deepest ethical convictions spring not from reason but from sentiment. Morality, he insisted, is not discovered through logical deduction. It is felt.

Published in 1751, An Enquiry Concerning the Principles of Morals represents Hume's mature statement on ethics. He considered it "of all my writings, historical, philosophical, or literary, incomparably the best." Philosophers have often preferred his earlier Treatise of Human Nature (1739-40), but the Enquiry offers a more polished treatment of his revolutionary ideas. It remains one of the most elegant and readable works in the history of moral philosophy.

To understand what Hume was doing, we need to understand what he was fighting against. Eighteenth-century moral philosophy was dominated by two opposing camps, both of which Hume found deeply unsatisfying.

The rationalists, following Samuel Clarke and William Wollaston, argued that moral truths are discovered through reason alone, much like mathematical truths. Just as we can prove that the angles of a triangle sum to 180 degrees, we can prove that lying is wrong. Moral knowledge is a species of intellectual knowledge. The person who acts immorally is making a cognitive error.

The egoists, most prominently Thomas Hobbes and Bernard Mandeville, took the opposite view. All human action, they claimed, is ultimately self-interested. When we appear to act benevolently, we're really pursuing our own pleasure, reputation, or advantage. Morality is a useful fiction, a set of conventions that serve our self-interest by enabling social cooperation. Strip away the veneer, and you'll find nothing but enlightened selfishness.

Hume rejected both positions. Against the rationalists, he argued that reason alone can never motivate action. Against the egoists, he insisted that genuine benevolence exists and cannot be explained away. The truth, he believed, lay in a third option that neither camp had adequately explored: the moral sentiments.

This sounds simple. Its implications are radical.

Consider what happens when you call an action "wrong." According to Hume, you are not describing a property of the action itself, the way you might describe a ball as red or round. You are expressing a sentiment of disapproval. The wrongness is not "out there" in the world waiting to be discovered. It is "in here," in the distinctive feeling that human psychology produces when confronted with certain kinds of behavior.

This does not make morality arbitrary or subjective in any simple sense. Human nature is remarkably uniform across cultures and historical periods. We share a common psychology that produces similar sentiments in response to similar situations. The person who feels no disapproval at gratuitous cruelty is not merely different from us. Something has gone wrong with their moral faculty, just as something has gone wrong with the color-blind person's visual faculty.

But it does mean that morality is grounded in human nature rather than in abstract reason or divine command. If we were constituted differently, if we lacked sympathy for others or felt pleasure at their suffering, our morality would be different too. There is no view from nowhere, no God's-eye perspective from which moral truths can be read off the structure of reality.

Hume's most famous claim appears in the earlier Treatise, but the Enquiry develops its implications for ethics.

Reason is, and ought only to be the slave of the passions.

What does this mean? Reason can tell you that a certain action will produce certain consequences. It can inform you that lying will damage your reputation, that exercise will improve your health, that studying will help you pass the exam. But reason alone cannot make you care about your reputation, your health, or your exam results. That caring comes from somewhere else: from the passions, desires, and sentiments that constitute your motivational structure.

Consider someone with antisocial personality disorder who understands perfectly well that his actions cause suffering. He can reason about consequences as well as anyone. What he lacks is the sentiment of sympathy that would make others' suffering matter to him. His reason is intact; his affective responses are impaired. This shows that moral motivation cannot be purely rational.

The implications extend beyond individual psychology. Hume is making a point about the logical structure of moral reasoning. You cannot derive an "ought" from an "is." No amount of factual information about the world can, by itself, generate a conclusion about what you should do. The facts must be combined with some sentiment, some caring, some valuation, before they can guide action.

Having established that morality rests on sentiment, Hume turns to a systematic analysis of which qualities we actually approve of and why. His method is empirical rather than a priori. Instead of deducing what virtue must be from abstract principles, he examines what qualities humans actually praise and blame.

The pattern he discovers is elegant. We approve of qualities that are either useful or agreeable, either to the person who possesses them or to others. This gives us four categories of virtue:

Qualities useful to others include justice, fidelity, honesty, and benevolence. We approve of these because they benefit society. A world of liars and cheats would be miserable for everyone. We have evolved and been socialized to feel approval toward traits that make social life possible.

Qualities useful to the possessor include prudence, industry, frugality, and enterprise. We approve of these because they benefit the individual who has them. Even when others don't directly gain, we feel a sympathetic pleasure at qualities that serve a person's own good.

Qualities agreeable to others include politeness, wit, modesty, and good humor. These don't produce utility in any narrow sense; they simply make social interaction pleasant. We enjoy being around people who have them and feel approval accordingly.

Qualities agreeable to the possessor include cheerfulness, self-esteem, and tranquility of mind. These make life enjoyable for the person who has them. Through sympathy, we share in that enjoyment and approve of the qualities that produce it.

This framework explains why different societies praise somewhat different virtues. The useful qualities will vary depending on circumstances. A warrior society will prize courage and ferocity; a commercial society will prize honesty and punctuality. But the underlying principle remains constant: we approve of what is useful or agreeable.

Hume devotes particular attention to justice and benevolence, the two great social virtues that make civilized life possible.

Benevolence is natural and immediate. When we see someone in distress, we feel an instinctive sympathy that motivates us to help. This requires no elaborate reasoning, no calculation of consequences. The sentiment arises spontaneously from our psychological constitution. Benevolence is what Hume calls a "natural virtue," one that would exist even outside society.

Justice is different. It is an "artificial virtue," a human invention that serves social utility. Consider property rights. There is nothing natural about the idea that this piece of land belongs to me and that piece belongs to you. The institution of property is a convention, developed because it serves everyone's long-term interests. Without secure property, no one would bother to cultivate land, build houses, or accumulate goods. Society would collapse into a war of all against all.

But if justice is artificial, why do we feel such strong moral sentiments about it? Hume's answer is that we come to approve of justice because we recognize its utility. We see that societies with stable property rights flourish while those without them descend into chaos. This recognition, combined with our sympathy for the beneficiaries of just institutions, produces a genuine moral sentiment. The artificial becomes naturalized through habit and education.

This explains why justice can sometimes seem to conflict with benevolence. The just thing to do (return the borrowed sword to its owner) might not be the benevolent thing to do (if the owner plans to use it for murder). Hume acknowledges these tensions without fully resolving them. His general view is that justice operates through general rules whose overall utility outweighs the occasional bad outcomes in particular cases. We must resist the temptation to violate just rules whenever we think we can produce better consequences, because this temptation is precisely what just rules are designed to constrain. Whether this fully answers the problem remains debated.

Buried in a paragraph of the Treatise, but implicit throughout the Enquiry, lies what may be Hume's most influential contribution to ethics: the is-ought problem.

"In every system of morality, which I have hitherto met with, I have always remarked, that the author proceeds for some time in the ordinary way of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when of a sudden I am surprised to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not."

The point is deceptively simple. You cannot derive a conclusion about what ought to be the case from premises that only describe what is the case. No amount of factual information, however complete, can by itself generate a moral conclusion. Something else is needed: a sentiment, a valuation, a caring about outcomes.

This observation (sometimes called "Hume's guillotine") has cut through centuries of moral philosophy. It challenges any attempt to ground ethics in pure reason, natural law, divine command, or scientific fact. Each of these approaches, Hume suggests, smuggles in a hidden evaluative premise. The natural law theorist assumes we ought to follow nature. The divine command theorist assumes we ought to obey God. The scientific ethicist assumes we ought to maximize well-being or minimize suffering. But these "oughts" cannot be derived from the "is" statements that precede them.

Scholars continue to debate exactly what Hume meant by this passage and how strong a claim he intended to make. Some read it as a logical point about the impossibility of deriving evaluative conclusions from purely descriptive premises. Others see it as a more modest observation about the need to make our evaluative premises explicit. Either way, the passage has shaped metaethics ever since.

How do we come to care about others' welfare? Hume's answer is sympathy, a psychological mechanism that allows us to share in the feelings of those around us.

Sympathy, for Hume, is not quite what we mean by the word today. It is not merely feeling sorry for someone. It is a process by which we come to experience, in attenuated form, the emotions of others. When we see someone in pain, we feel a faint echo of that pain ourselves. When we see someone joyful, we share in their joy. This mirroring of feeling is automatic and largely involuntary.

Sympathy explains why we approve of qualities that benefit others. When someone's benevolence produces happiness in those around them, we sympathize with that happiness. The pleasure we feel through sympathy becomes associated with the quality that produced it. We come to approve of benevolence because contemplating it produces pleasant sentiments in us.

But sympathy has limits. We sympathize more easily with those close to us, those similar to us, those whose situations we can vividly imagine. A child drowning in front of us produces far more sympathy than thousands dying in a distant famine. This is not necessarily a moral failing; it is simply how human psychology works.

Hume acknowledges this partiality and argues that moral judgment requires correcting for it. When we make moral assessments, we adopt a "general point of view," abstracting from our particular position and considering how a quality would appear to anyone. This doesn't eliminate sympathy; it extends and generalizes it. We imaginatively take up the perspective of all those affected by an action, not just those we happen to care about most.

Hume's sentimentalism has faced powerful criticisms over the centuries.

The relativism objection. If morality is based on sentiment, and sentiments vary across cultures and individuals, doesn't this make morality relative? What's wrong for me might be right for you, depending on how we feel.

Hume's response: Human nature is remarkably uniform. We share the same basic psychological constitution, the same capacity for sympathy, the same tendency to approve of useful and agreeable qualities. Variations exist, but they are variations on a common theme. Moreover, many apparent moral disagreements are really factual disagreements: we agree that we should help others flourish but disagree about what flourishing requires. Critics note, however, that this response may underestimate the depth of genuine moral disagreement across cultures and historical periods.

The motivation objection. Hume claims reason cannot motivate action. But surely we sometimes act on purely rational considerations, overriding our feelings because we recognize what's right.

Hume's response: Look more carefully at these cases. When you override a present desire for the sake of future benefit, you are not acting on pure reason. You are acting on a desire for future benefit that happens to be stronger than the present desire. Reason helps you see the consequences; sentiment provides the caring. Even the most "rational" action is ultimately motivated by some passion. This remains one of the most contested points in moral psychology, with Kantians arguing that practical reason can motivate independently of desire.

The authority objection. If morality is just a matter of sentiment, what gives it authority over us? Why should I care about what produces approval in others?

This is perhaps the deepest challenge. Hume's answer is that morality has no authority beyond the sentiments themselves. If you genuinely lack the moral sentiments, if you feel no sympathy for others and no approval of virtue, then morality has no grip on you. But such people are rare and typically recognized as pathological. For the rest of us, the sentiments are simply there, part of our constitution, shaping our responses whether we like it or not. Many philosophers find this answer unsatisfying, arguing that it fails to capture the distinctive normativity of moral claims.

Hume's insights remain relevant to contemporary life, though their application requires care.

In business and leadership, the recognition that reason alone cannot motivate has practical implications. You cannot lead people by presenting arguments alone; you must engage their concerns and values. The most brilliant strategic plan will fail if it doesn't connect with what people actually care about. Facts and logic matter, but they work best when they speak to existing motivations.

In technology and AI ethics, Hume's framework raises interesting questions. We increasingly rely on algorithms to make decisions that affect human welfare. But algorithms operate through calculation; they have no sentiments. An AI system can be programmed to maximize a metric, but it cannot care about the outcomes in the way humans do. Whether this represents a fundamental limitation or merely a current technological constraint remains debated.

In political discourse, Hume helps explain why rational argument often fails to persuade. When people's beliefs are grounded in deep-seated values and identities, presenting contrary facts may not change their minds. This is not necessarily irrational; it may reflect the priority of sentiment over reason in moral judgment. Understanding this can help us approach disagreement with more patience, recognizing that persuasion often requires finding common ground in shared values rather than simply marshaling evidence.

In personal relationships, Hume's emphasis on sympathy highlights what makes intimacy possible. We connect with others not primarily through rational agreement but through shared feeling. The friend who understands your suffering, the partner who shares your joys: these relationships are built on sympathetic resonance.

In understanding ourselves, Hume offers an alternative to the picture of humans as primarily rational agents. You are not a purely rational being who happens to have inconvenient emotions. You are a feeling being whose reason serves your passions. This is not a defect to be overcome but the basic structure of human psychology. Accepting it allows you to work with your nature rather than against it.

Modern research in moral psychology has provided some support for Hume's core claims, though the picture is more complex than a simple vindication.

Studies of moral judgment consistently find that emotional responses play a significant role in shaping our moral intuitions. Jonathan Haidt's influential research suggests that we often reach moral conclusions intuitively and then construct rational justifications after the fact. This echoes Hume's view that sentiment precedes and shapes reasoning.

Research on individuals with damage to brain regions associated with emotion (particularly the ventromedial prefrontal cortex) shows impairments in moral judgment, suggesting that emotion is not merely incidental to moral cognition. Similarly, studies of psychopathy confirm that deficits in emotional responsiveness are associated with impaired moral motivation, even when moral knowledge remains intact.

The discovery of mirror neurons in the 1990s has provided one possible neural mechanism for sympathy. When we observe others' actions and emotions, neurons fire in our brains in patterns similar to those that would occur if we were performing those actions ourselves. However, the exact role of mirror neurons in empathy and moral cognition remains a matter of ongoing research.

Research on moral intuitions has revealed that people's judgments are influenced by factors they cannot articulate and might not endorse if made explicit: the order in which options are presented, incidental emotions, and various framing effects. This suggests that moral judgment is more intuitive and less purely rational than many assume, though it does not settle the question of whether reason can or should override these intuitions.

Hume's influence on subsequent ethics is immense, though often unacknowledged.

The utilitarian tradition, developed by Jeremy Bentham and John Stuart Mill, owes much to Hume's emphasis on utility and his naturalistic approach to ethics. Mill explicitly acknowledged his debt to Hume's analysis of justice and benevolence.

Emotivism, the twentieth-century view that moral statements express attitudes rather than describe facts, is Hume's sentimentalism in analytic dress. A.J. Ayer and Charles Stevenson developed sophisticated versions of this view, arguing that "X is wrong" expresses disapproval rather than stating a fact.

Contemporary moral psychology, led by figures like Jonathan Haidt, has returned to Hume with enthusiasm. Haidt's "social intuitionist model" argues that moral judgment is primarily driven by intuition and emotion, with reasoning serving mainly to justify conclusions already reached. This is recognizably Humean, updated with modern experimental evidence.

The effective altruism movement, despite its emphasis on rational calculation, ultimately depends on Humean sentiments. You cannot reason your way to caring about strangers' suffering; that caring must come from somewhere else. What reason can do is extend and direct the caring you already have.

Even Kant, Hume's great philosophical opponent, was shaped by the encounter. Kant famously said that Hume awoke him from his "dogmatic slumber." The entire Kantian project of grounding morality in pure reason can be read as a response to Hume's challenge. Whether Kant succeeded remains contested, but the terms of the debate were set by Hume.

• Hume's A Treatise of Human Nature, especially Book III, offers a more detailed but less polished treatment of the same themes. Essential for serious students of Hume's ethics.

• Adam Smith's The Theory of Moral Sentiments develops Humean themes with particular attention to sympathy and the "impartial spectator." Smith was Hume's close friend and intellectual heir.

• Jonathan Haidt's The Righteous Mind brings Hume's psychology into the twenty-first century, arguing that moral judgment is primarily intuitive and that reason serves mainly as a lawyer for our intuitions.

• Simon Blackburn's Ruling Passions offers a sophisticated contemporary defense of Humean sentimentalism, engaging with technical debates in metaethics while remaining accessible.

• Annette Baier's A Progress of Sentiments provides a careful reading of Hume's moral philosophy, emphasizing its connections to his broader epistemology and his account of human nature.