Skeptical Doubts
The Problem of Induction
| § | David Hume | Karl Popper The Logic of Scientific Discovery | Bertrand Russell The Problems of Philosophy | A.J. Ayer Language, Truth and Logic | W.V.O. Quine Two Dogmas of Empiricism |
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| §1 | The Problem of InductionAll reasonings concerning matter of fact seem to be founded on the relation of Cause and Effect. By means of that relation alone we can go beyond the evidence of our memory and senses. If you were to ask a man, why he believes any matter of fact which is absent; he would give you a reason; and this reason would be some other fact, connected with it. But as this fact, in its turn, is connected with some other by the same relation of cause and effect, the man would be obliged to proceed without end, unless he could rest on some principle of connexion betwixt facts, founded not on the relation of ideas, nor on any matter of fact. I say then, that even after we have experience of the operations of cause and effect, our conclusions from that experience are not founded on reasoning, or any process of the understanding. The supposition that the future will resemble the past, is not founded on arguments of any kind, but is derived entirely from habit. | Hume has indeed identified a fatal flaw in induction, but his conclusion should be more radical: induction does not exist as a rational process. Science does not proceed by induction—by generalizing from observed instances to universal laws. Instead, science proceeds by conjecture and refutation. We propose bold hypotheses (not derived from observations) and then test them through attempts at falsification. Scientific theories are never verified or confirmed; they are only corroborated by surviving severe tests. Hume's argument shows that induction cannot provide rational justification, which is why we must abandon inductivism entirely in favor of a deductivist methodology based on falsification. | Hume's problem of induction is one of the most profound difficulties in philosophy. We do assume that nature is uniform—that unobserved instances will resemble observed instances—but we cannot prove this assumption. It is not a logical truth (its denial involves no contradiction), and we cannot establish it empirically without circularity (using past uniformity to prove future uniformity). Yet all science depends on induction. My own solution involves accepting the principle of induction as a postulate that cannot be proved but must be assumed if we are to have any empirical knowledge. This is not fully satisfying, but it is the most honest response to Hume's devastating argument. | Hume is correct that inductive inference cannot be justified by appeal to experience without circularity, nor by a priori reasoning. But this does not mean that induction is irrational. The problem dissolves when we recognize that asking for a justification of induction is like asking for a justification of deduction—it is asking for what cannot coherently be given. To call an inference inductive just is to say that it conforms to inductive standards of reasoning. We cannot justify induction in terms of something more fundamental because induction is itself fundamental to empirical reasoning. The problem of induction is a pseudo-problem arising from unreasonable demands for justification. | Hume's problem points to the holistic nature of empirical knowledge. There is no sharp boundary between matters of fact (justified by experience) and relations of ideas (justified by logic). All our beliefs face the tribunal of experience together, and no single belief—including the principle of induction—can be confirmed or disconfirmed in isolation. The uniformity of nature is not a separate assumption that must be justified, but part of the overall web of belief that we adjust to accommodate recalcitrant experience. When we engage in induction, we are not applying a questionable principle but participating in our ongoing project of making sense of experience holistically. The problem of induction vanishes when we abandon the analytic-synthetic distinction and embrace epistemological holism. |
| §2 | Necessary ConnectionWhen we entertain, therefore, any suspicion that a philosophical term is employed without any meaning or idea (as is but too frequent), we need but enquire, from what impression is that supposed idea derived? And if it be impossible to assign any, this will serve to confirm our suspicion. By bringing ideas into so clear a light we may reasonably hope to remove all dispute, which may arise, concerning their nature and reality. It is universally allowed that nothing exists without a cause of its existence, and that chance, when strictly examined, is a mere negative word, and means not any real power which has anywhere a being in nature. But here arises a difficulty. By what right do we assert that everything that begins to exist must have a cause? This proposition neither is nor ever can be demonstrated. Its evidence is not intuitive; for if it were, it would be a contradiction to deny it. | Hume is absolutely right that we cannot observe necessary connection or prove that particular causal laws must hold. But he is wrong to conclude that our belief in causation is merely habit. Scientific theories assert causal regularities as bold conjectures that go beyond observed conjunctions. These theories are not derived from observations by induction but are creative hypotheses that we test empirically. When a theory survives severe tests, we have reason to believe it—not certainty, but rational grounds for tentative acceptance. Causation is not habit but conjecture, and causal knowledge is possible through the method of conjecture and refutation, even though Hume shows that it cannot be obtained through induction. | Hume's analysis of causation is devastating to rationalism but also to uncritical empiricism. We do not perceive necessary connection; we only perceive constant conjunction. This means that causal laws are not necessarily true—they could be otherwise without logical contradiction. However, I would not go as far as Hume in reducing causation to mere habit. There are lawful regularities in nature, even if we cannot prove their necessity. The project of science is to discover these regularities and formulate them as general laws, even though we cannot demonstrate that they must hold. Hume shows the limits of what we can know with certainty, but he need not lead us to complete skepticism about causation. | Hume's critique of necessary connection points toward the correct analysis of causal statements. To say that A causes B is not to describe some mysterious necessary connection but to assert that events of type A are invariably followed by events of type B. Causal statements are generalizations about regularities in experience. The idea of necessary connection is indeed spurious if it means something beyond constant conjunction. However, we can reformulate causation in terms of laws—universal conditional statements that support counterfactuals. The statement 'A causes B' means not just that A is followed by B, but that if A were to occur (even in cases where it doesn't), B would follow. This analysis preserves the predictive content of causal claims without invoking metaphysical necessity. | Hume's empiricist scruples about necessary connection are admirable but can be taken too far. In our best scientific theories, causal relations are embedded in networks of laws and theoretical principles. These principles face experience as a corporate body, not individually. When we assert a causal claim, we are not merely reporting observed regularities but invoking a theoretical framework that explains and predicts phenomena. The necessity in causal claims is not metaphysical but stems from their role in our theory—they are deeply embedded, relatively immune to revision. Hume is right that experience alone cannot establish necessity, but necessity can emerge from the systematic character of our scientific theories. |