David Hume: How Empiricism Leads to Scepticism

This is the fifth article in the series Understanding Philosophy: Thinkers, Questions and Ideas. The previous article examined Descartes’ attempt to find an indestructible rational beginning within doubt. This one turns to David Hume and asks why causation, the self and the certainty of the world become unstable when knowledge is strictly limited to what experience can provide.

Empiricism initially appears cautious and secure. Instead of deducing the world from abstract principles, it tells us to observe experience. Instead of assuming that the mind arrives equipped with a large stock of innate ideas, it asks where each idea comes from. Hume applies these demands with exceptional consistency, but the result is not a stronger system of certain knowledge. Many beliefs indispensable to ordinary life and scientific reasoning prove to contain elements that experience cannot fully justify. In this way empiricism leads towards scepticism.

Hume begins by distinguishing impressions from ideas. Impressions are the more vivid perceptions of present sensation, emotion and desire: seeing red, feeling pain or undergoing anger. Ideas are fainter reappearances of such experiences in memory and thought. The mind can combine ideas and imagine things never encountered, such as a golden mountain or a winged horse. Yet the basic materials of these inventions still derive from prior impressions. This “copy principle” supplies a test for concepts. If a word has no experiential source that can be identified, we should ask whether we have given it any clear meaning.

The principle does not reduce the mind to a passive storehouse. Ideas become associated through resemblance, proximity in time or place, and relations of cause and effect. Memory and imagination organise experiential materials into a continuous world rather than an unrelated sequence of sensations. Hume’s question is how much of that connection belongs to the objects themselves and how much results from habits acquired by the mind. The fact that a relation feels entirely natural in thought does not by itself show that we have discovered a corresponding necessity in reality.

Hume further distinguishes relations of ideas from matters of fact. Mathematics and logic belong to the first group. Their denial produces a contradiction, and their truth can be established without observing the world. That three multiplied by five equals fifteen is guaranteed by relations among the concepts. Matters of fact are different. There is no logical contradiction in denying that the sun will rise tomorrow. We believe very strongly that it will rise, but we do not reach that belief simply by analysing the relevant concepts.

Reasoning about matters of fact depends upon causation. We expect heat from flame, rain from dark clouds and future events to resemble established patterns. Yet experience directly presents only one event repeatedly following another. We see a flame and subsequently feel heat, but we never see a separate item called a necessary connection binding the two. No matter how frequently a sequence has been observed, experience reports what happened in the past. By itself it cannot prove that the future must continue in the same way.

This produces the problem of induction. We ordinarily assume that nature is sufficiently uniform for patterns established in the past to remain valid under similar conditions. But if we use the past success of induction to prove that nature will continue to be uniform, we have already assumed the principle we wanted to justify. Induction cannot be demonstrated by pure logic, and experience cannot prove it without circularity. Hume does not tell us to stop predicting. He shows that prediction ultimately rests not on a rational perception of necessity but on expectations formed through repeated experience.

Causal belief therefore emerges from custom. When two events occur together repeatedly, encountering the first naturally carries the mind towards the second, and the felt force of that transition is experienced as necessary connection. Custom is not an optional intellectual defect. It is a basic mechanism through which human beings and other animals can act in the world. Without it we could not learn from experience or prepare for the next moment. What scepticism reveals is not that life must cease, but that the cognitive mechanism on which life depends is not the same as a strict proof.

Hume’s account of the self has the same structure. When he looks inward, he finds particular perceptions: warmth, cold, pleasure, pain, memories, desires and thoughts. He does not encounter a constant self appearing separately from every perception. The self looks more like a bundle of changing but related perceptions. Memory, resemblance and causal narrative allow these experiences to be understood as the continuous life of one person, but experience does not directly present an unchanging subject-substance beneath them.

This does not imply that persons do not exist or that ordinary identity is simply false. Hume asks whether experience justifies conceiving of the self as simple, constant and independent. When we observe a river, we use one name for a flow whose water continually changes. Personal identity might likewise depend upon relations within change rather than an unaltered core hidden behind it. Scepticism does not remove the living person. It changes the philosophical account of that person’s unity.

Belief in the external world cannot receive an absolute proof either. We naturally believe that objects continue to exist when no one perceives them, but what is immediately present to the mind remains perception. If we attempt to infer independent objects from perceptions, we must explain why that inference is reliable. Hume thinks nature makes belief in a continuing world unavoidable, while philosophical argument struggles to give that belief a Cartesian foundation of certainty. Reason can disclose the limits of belief without being able to erase a natural human disposition.

Hume’s scepticism is therefore not nihilism. He does not claim that every view is equally good, and he does not recommend rejecting science or ordinary experience. He distinguishes excessive scepticism from a more moderate form. A radical doubt that tried to suspend all belief in practical life would quickly be interrupted by hunger, conversation, habit and life itself. Moderate scepticism instead restrains the degree of confidence, adjusts judgement to the available evidence and warns against large conclusions that reach beyond experience.

This position is often described as naturalism. Human beings do not first prove causation, the world and other minds philosophically and only then begin to believe in them. Such beliefs belong to human cognitive life. Philosophy can explain how they arise, where they work and why they should not be mistaken for logical necessities, but it cannot lift us entirely outside nature. In the study, Hume can press doubt to its limits. Among friends, games and dinner, ordinary belief naturally returns. This is not merely personal weakness; it forms part of his theoretical conclusion.

In morality, Hume similarly rejects the idea that reason is the sole motive force. Reason can inform us about facts and means, but it cannot generate the ends of action by itself. Moral judgement is connected with feeling, sympathy and responsiveness to the happiness and suffering of others. This does not make morality an arbitrary preference, because human beings possess shared emotional capacities that can be communicated, widened and corrected. It means that moral life cannot be deduced from pure logic. Knowing a fact and caring about it are not the same activity.

Hume leads empiricism into scepticism because he refuses to insert guarantees at precisely the points where experience does not supply them. Necessary causation, a substantial self, the uniformity of nature and moral purposes cannot receive philosophical legitimacy merely because ordinary language assumes them. The cost is a reduction in certainty. The gain is a more honest account of human cognition. We know less than we may have imagined, but the processes through which we believe, expect and act become more intelligible.

Kant later wrote that Hume had interrupted his “dogmatic slumber”. Hume’s challenge forced subsequent philosophy to reconsider the source of necessity. If experience cannot provide necessity, yet scientific knowledge requires universal structures, where do those structures come from? Whether or not Kant’s answer is accepted, Hume had already changed the form of the question. Philosophy could no longer treat a belief’s long practical success as if that alone constituted a proof.

Empiricism’s movement towards scepticism is not simply a failure. It is the result of taking its own principles seriously. Hume shows that experience gives us events but not necessity, a sequence of perceptions but not directly a permanent self, and a past but no guarantee of the future. Human beings continue to live, investigate and judge, but certainty can no longer come from a promise beyond experience. It must remain constrained by the reach of evidence, the work of habit and the limits of human cognition.