A Treatise of Human Nature

Quick Facts

• Author: David Hume
• Full title: A Treatise of Human Nature: Being an Attempt to Introduce the Experimental Method of Reasoning into Moral Subjects
• First published: 1739-1740, anonymously
• Structure: Book 1, "Of the Understanding"; Book 2, "Of the Passions"; Book 3, "Of Morals"
• Main problem: how to build a science of human nature from experience instead of speculation.
• Main traditions: Empiricism, Skepticism, Scottish Enlightenment

In One Minute

Hume's Treatise asks what human beings are actually doing when they think, believe, desire, judge, and call things moral. His answer is blunt: start with experience. The mind is not filled with innate ideas or hidden rational powers. It receives vivid experiences, makes weaker copies of them, links them by habit, and then lives from the beliefs, passions, and moral feelings that result.

That makes the book both ambitious and unsettling. Hume wants a science of human nature, but that science shows that many strong beliefs are not grounded in rational proof. We believe in causation because repeated patterns train expectation. We believe in a continuing self because memory and imagination link changing experiences into one story. We act because passions move us. We judge morally because we feel approval or disapproval from a shared human point of view.

The Problem

Hume thinks philosophy has argued for too long with unclear words. People talk about substance, self, cause, free will, moral obligation, and reason as if these labels name obvious things. Hume asks a simpler question: what experience gives us these ideas?

This is why the subtitle matters. Hume wants to bring the experimental method into "moral subjects," meaning subjects about human beings: mind, action, emotions, society, and morality. His method is observation of ordinary life. Watch how people reason, remember, expect, love, resent, praise, blame, promise, and obey rules. Then explain the mental principles that make those patterns possible.

The hard part is that this method threatens the old ambitions of philosophy. If every meaningful idea must trace back to experience, then we need to ask whether we have any impression of necessary causation, a permanent self, moral facts grasped by reason alone, or a purely rational motive to act. Hume's answer is usually no. Then he explains why human beings naturally believe and act anyway.

The Main Argument

Hume begins with perceptions, his broad word for whatever appears in the mind. Impressions are vivid experiences: seeing a candle flame, feeling heat, tasting wine, or feeling anger. Ideas are fainter copies or recombinations: remembering the flame, imagining heat, or picturing a golden mountain from prior ideas of gold and mountains. If an idea cannot be traced back to any impression, Hume suspects that philosophy has made a word look deeper than it is.

Next, Hume explains how ideas connect. Association is the mind's tendency to move from one perception to another. The three central associative links are resemblance, closeness in time or place, and cause and effect. A portrait makes you think of the person it resembles. A room in your old school makes you think of the hallway next to it. Smoke makes you think of fire.

Causation is the crucial case. We think causes produce effects with necessity. But experience gives us one event followed by another, not a visible power tying them together. A billiard ball strikes another ball; the second ball moves. A flame touches paper; the paper burns. The senses show sequence and repetition, not an extra object called necessary connection.

Hume's explanation is habit. When one kind of event is constantly followed by another, the mind becomes trained to expect the second when the first appears. That expectation is belief. Belief is not just a pale idea; it is an idea made lively by its connection to a present impression. Seeing dark clouds makes rain feel likely because past experience has joined clouds and rain in the imagination.

This creates the problem of induction. Induction means reasoning from observed cases to unobserved cases: bread nourished me before, so this bread will nourish me; the sun rose before, so it will rise tomorrow. Hume argues that reason cannot prove this step. We rely on induction because custom carries us forward, not because reason has demonstrated it once and for all.

Hume applies the same pressure to the self. When he looks inward, he finds particular perceptions: warmth, pain, memory, hope, pride, fear. He does not find a separate impression of a permanent soul-like owner behind them. The bundle theory of self says the self we experience is a bundle of changing perceptions linked by memory, resemblance, and causal relations.

Book 2 turns to passions. Passions are felt motives and emotions: desire, fear, joy, grief, pride, humility, love, hatred. Hume does not treat them as irrational noise added to an otherwise rational machine. They are central to action. Reason can tell you that a medicine will reduce pain or that an insult was accidental. But reason by itself does not make you want health, safety, friendship, revenge, or peace. Passion supplies the push; reason helps find the route.

Book 3 uses that psychology to explain morality. Reason can discover facts: who lied, who was harmed, what promise was made. But after the facts are known, moral judgment appears through sentiment. Moral sentiment is the feeling of approval or disapproval we have when we view a character trait or action from a steadier, more general point of view. Courage, honesty, kindness, and justice please us because of how they affect people.

Sympathy is the mechanism that lets the feelings and interests of others matter to us. If you see someone humiliated, you can feel discomfort on their behalf. Sympathy helps explain why morality is not just private appetite.

Hume's famous is/ought point belongs here. Writers often move from claims about what is the case to claims about what ought to be done, as if the step were automatic. Hume says that step needs explanation. Facts matter, but facts alone do not generate obligation.

Why It Matters

The Treatise changes the target of philosophy. Instead of asking what reason can prove from the armchair, Hume asks how the human mind actually works.

Its account of causation and induction is the classic Humean challenge. Science depends on learning from observed patterns, but Hume shows that this practice rests on habit and expectation rather than deductive certainty. This makes science look fallible, experimental, and tied to evidence instead of metaphysical guarantees.

The book also reshapes moral philosophy. Hume gives a secular account of morality built from human feeling, sympathy, usefulness, and social life. Justice is not a mysterious eternal object. It is a set of rules useful for creatures like us, with limited generosity and limited resources.

The personal identity argument matters because it attacks the idea that introspection reveals a simple, permanent self. Later debates about the mind and personal identity keep returning to Hume's pressure.

Key Ideas With Examples

• Impressions: vivid experiences as they happen. The burn of hot coffee, the red of a stop sign, and the anger in an argument are impressions.
• Ideas: fainter copies or recombinations of impressions. Remembering the coffee, picturing the sign, or imagining tomorrow's argument are ideas.
• Copy principle: meaningful simple ideas come from impressions. A golden mountain is built from prior experiences of gold and mountains.
• Association: the mind's habit of linking perceptions. A wedding song recalls a person; thunder makes you expect rain.
• Causation: our expectation that one kind of event brings another. Hume says we observe flame followed by heat, then the mind adds expectation.
• Induction: moving from past cases to new cases. You expect the next apple to taste like earlier apples, but that expectation is not deductively proven.
• Belief: an idea made lively by a present impression and habit. Dark clouds make rain feel more real than a bare thought of rain.
• Bundle theory of self: the self is the connected stream of perceptions, memories, feelings, bodily continuities, and social relations we treat as one person.
• Passions: emotions and motives that move us to act. Fear makes you step back; love makes another person's good matter to you.
• Reason and passion: reason discovers truths and means, but passion supplies ends. Reason can find the safer path only after you care about safety.
• Sympathy: the capacity to take up another person's feeling or interest. A friend's disappointment can make you feel discomfort too.
• Moral sentiment: approval or disapproval from a general human standpoint. You approve of honesty because you feel the value of trust in shared life.
• Is/ought: facts do not automatically yield moral conclusions. "This rule benefits the powerful" does not prove "therefore it ought to be obeyed."

Common Confusions

• Hume is not saying experience is worthless. He is saying it works through habit, probability, and human nature, not perfect proof.
• Hume is not denying that causes exist in ordinary life. He is denying that we perceive a hidden necessary power in the cause itself.
• The bundle theory does not mean people are unreal. It means the self is not an extra simple substance discovered behind experience.
• "Passion" does not mean wild emotion only. Hume includes calm motives and settled preferences.
• Hume is not saying morality is arbitrary. Moral judgment depends on shared human nature, sympathy, usefulness, and common points of view.
• The is/ought point is not that facts are irrelevant to ethics. Facts are necessary; they just do not do the whole job.

People And Schools

David Hume wrote the Treatise as his most ambitious attempt to explain the mind, passions, and morals together. It did not get the reception he wanted.

The work belongs to Empiricism because it tests ideas by tracing them to experience. It belongs to Skepticism because it limits what reason can honestly claim. It is also a Scottish Enlightenment work because it treats human nature and society as subjects for disciplined inquiry.

John Locke is the major background figure. In An Essay Concerning Human Understanding, Locke made experience central to ideas. Hume radicalizes that approach by applying it to causation, selfhood, belief, and morality.

George Berkeley is another background pressure. Berkeley had attacked abstract ideas and pushed empiricism in an anti-materialist direction. Hume keeps the pressure against empty abstractions but does not use Berkeley's theology as a rescue.

Francis Hutcheson matters for the moral side. Hume develops a moral-sentiment approach, but gives it a broader psychology of sympathy, utility, passions, and social convention. Isaac Newton matters as a model for method.

Critics And Reactions

The first reaction was muted and often hostile. Hume later thought the book had gone to press too early. He recast Book 1 in An Enquiry Concerning Human Understanding and Book 3 in Enquiry Concerning Principles of Morals.

Immanuel Kant is the most famous later respondent. In the Critique of Pure Reason, Kant argues that causation is not merely habit from repeated experience but a basic rule the mind uses to make objective experience possible.

Common-sense philosophers such as Thomas Reid objected that Hume's skepticism undercut perception, memory, and personal identity. Religious critics disliked the broader project because it explained belief, morality, and human life without grounding them in theology.

Later philosophers kept returning to the Treatise because it poses problems that do not go away: how induction is justified, what causation adds to regular sequence, whether the self is more than psychological continuity, whether reason can motivate action, and whether morality rests on sentiment or reason.

Related Pages

• David Hume
• Empiricism
• Skepticism
• An Essay Concerning Human Understanding
• George Berkeley
• John Locke
• Francis Hutcheson
• Isaac Newton
• An Enquiry Concerning Human Understanding
• Enquiry Concerning Principles of Morals
• Immanuel Kant
• Critique of Pure Reason