Habit, causation and the self

Before the kettle boils

Imagine Keiko switching on her kettle and taking a cup from the cupboard. The water is still cold, but she expects it to heat; earlier mornings guide what she does now.

The previous lesson asked what experience allows us to claim about a material world. David Hume asks how experience carries us beyond what we currently perceive or remember. Induction, in this setting, means reasoning from observed cases to cases we have not observed. What supports that step?

Two kinds of question

Hume distinguishes relations of ideas from matters of fact. Denying that three times five equals fifteen conflicts with the relation between the numbers; denying that the kettle will heat the water involves no such contradiction. So even a firmly supported prediction differs from a mathematical demonstration. [1]

Inferences about matters of fact beyond present sense and memory, Hume argues, depend on cause and effect. We hear a familiar voice and infer that a friend is nearby; we see smoke and expect fire. Such inferences can concern an unseen present or past as well as the future.

How do we learn these connections? From experience. Someone entirely unfamiliar with fire could not deduce its effects from its appearance alone. Knowing more about a kettle’s mechanism helps us predict its behavior, but that knowledge, too, rests on experience of how things work.

From past cases to the next

Keiko has seen this kind of kettle heat water many times. Those observations tell her what happened then; her prediction adds a claim about what will happen now. Why should the observed pattern extend to this case?

Hume considers two possible answers. A demonstration cannot establish that nature must continue uniformly, because a change in its course contains no contradiction. An argument from experience seems more promising: relying on past patterns has worked before. Yet that answer relies on the very step in question, since it moves from past success to future reliability. [1]

The difficulty goes deeper than a faulty kettle. Checking the wiring or adding more observations can improve a particular prediction, but each improved prediction still extends what we have learned to a case we have yet to observe, so we have not escaped the question of what supports that extension. Saying that the water will probably heat still leaves us asking why past experience makes it probable.

Custom carries us forward

If no argument supplies the missing foundation, what carries us from an observation to an expectation? Hume’s answer is custom, or habit, formed by repeated experience: seeing one event brings an expectation of its familiar companion. Keiko does not work through a proof each time she fills the kettle. Her experience has shaped how she anticipates what comes next. [1]

This explains why we believe; it does not demonstrate that the future must resemble the past. Believing also differs from freely imagining. Keiko can picture the water staying cold, but she cannot simply choose to expect that outcome with the same confidence.

Skeptical reflection therefore need not bring ordinary life to a halt. Hume says that custom goes on guiding action even when its foundation puzzles us. We can examine circumstances, correct mistakes and learn from further experience, and the lack of the proof we wanted does not make every expectation equally well informed.

The feeling of connection

What, then, do we mean by a necessary connection? We seem to mean a tie that makes an effect follow from its cause, rather than merely happen afterward. Hume asks what experience could give us this idea. [1]

Watching one event follow another reveals a sequence, and repeating the observation reveals no previously hidden tie in any single pair. What changes is the observer’s response: one event now brings the expected effect to mind. Hume identifies that felt movement as the impression from which our idea of necessary connection arises. An impression here is an immediate experience, including something felt inwardly.

This locates the source of our idea. Feeling compelled to expect hot water does not give Keiko direct access to a power that guarantees it. The larger interpretive dispute, over what Hume permits us to say about powers beyond our experience, stays open here.

A self among its experiences

In his earlier Treatise, Hume puts a similar question to the self: what impression supplies the idea of a simple, unchanging subject behind our experiences? Looking inward, he finds particular perceptions—warmth, discomfort, affection, a thought—rather than a further, unvarying self. His word perception covers thoughts and feelings as well as sensations. [2]

His bundle account describes the mind as a succession of different perceptions, and the important question becomes how we come to regard them as one continuing person. Memory brings back images of earlier experiences, and the resemblance between a memory and the experience it recalls helps thought pass from one to the other. We also connect experiences through their effects on one another, as when Keiko recalls yesterday’s worry and how resolving it led to today’s relief.

This does not limit identity to what memory reaches: Hume explicitly allows us to connect a person’s life across forgotten events. Nor does the argument settle every question about responsibility or concern for others. Its immediate target is the supposed direct awareness of a perfectly simple, enduring self.

A difficulty Hume kept open

In the Treatise appendix, Hume later admits that his account leaves him unable to explain satisfactorily how distinct perceptions belong together. He holds on to two commitments: distinct perceptions are distinct existences, and we do not perceive a real connection between distinct existences. He cannot reconcile them with a satisfactory account of how the perceptions form one mind. [2]

The problem therefore lies within the bundle account itself. To call the account Hume’s final proof that people are unreal would hide the very difficulty he records.

Try the explanation

Keiko says, “The kettle has always heated the water, so experience proves it must do so again. If Hume rejects that proof, I should expect nothing—and forgetting yesterday would mean I am a different person.” Repair the three claims. This exercise is optional.

Read a possible response

None of the three claims holds as stated. First, past observations establish past cases; extending their pattern to a new case requires the very step Hume questions. Invoking the previous success of that step uses it again, so it does not supply an independent proof. Second, doubt about that ultimate foundation does not require expecting nothing: custom still produces expectations, and further experience can help Keiko tell reliable conditions from misleading ones. Third, Hume does not make personal identity depend on remembering every event. Memory helps us recognize relations between experiences, and thought can extend those connections across forgotten periods; his challenge concerns an unchanging self supposedly perceived behind those experiences, and his appendix acknowledges a remaining problem in explaining their unity.

Carry this forward

Keep an explanation of why we believe something separate from a justification of its truth. Hume makes that distinction hard to ignore without asking us to leave ordinary life behind. Why should anyone obey a government? turns to political authority and asks what could justify a government’s claim to our obedience.

Sources and limits

[1] David Hume, An Enquiry concerning Human Understanding, IV, V and selected VII, Hume Texts Online, edited by Amyas Merivale and Peter Millican, for induction, custom and necessary connection. A locator such as IV.19 means section four, paragraph nineteen. Read:

• Sections IV and V: IV.1–23 and V.1–22, with V.5 note 8, paragraphs 1–5. IV.19 gives the circularity argument, and V.2–8 connects custom with ordinary life.
• Necessary connection: VII.4–8 and VII.26–30.

[2] Hume, A Treatise of Human Nature, I.iv.6, paragraphs 1–23, especially 1–6 and 15–22, and Appendix 10–21, especially 20–21, for the bundle account. I.iv.6 means Book I, part four, section six. These selections concern identity in thought and its acknowledged difficulty; they are not a complete account of Hume’s philosophy of persons.

The editors identify the copytext of the Enquiry as the 1777 Essays and Treatises, and the copytexts of the Treatise as the 1739–1740 publications. Both sources are original English texts, not translations. Neither work was read complete, and no comparison with the original printings was made. Sources accessed 18 September 2026. Keiko and the exercise are original teaching material. No independent scholarly review or learner testing is claimed.