Locke, Hume, and the Principle of Causality

LOCKE, HUME, AND THE PRINCIPLE OF CAUSALITY IN BOOK I of his Treatise, in a section entitled "Why a cause is always necessary," 1 Hume presents several logical attacks on the principle of efficient causality. These attacks purport to show that the causal principle is neither intuitively nor demonstratively certain and can be denied without a contradiction. The purpose of this paper is to analyze and evaluate one of these logical criticisms. Prefacing his logical analysis of the causal principle, Hume says: 'Tis a general maxim in philosophy, that whatever begins to exist, must have a cause of existence. This is commonly taken for granted in all reasonings, without any proof given or demanded. 'Tis suppos 'd to be founded on intuition, and to be one of those maxims, which tho' they may be deny'd with the lips, 'tis impossible for men in their hearts really to doubt of.2 The causal principle is thus an assumption " taken for granted " by philosophers. It is thought to be an axiom of the mind, " founded on intuition," and indubitably true.3 Hume then proceeds to analyze several demonstrations which have been put forth in defense of the causal principle. Three philosophers are singled out, viz., Hobbes, Clarke, and Locke. Hume claims that the fallacy of petitio principii is common to all of their arguments. It is his treatment of Locke's demonstration that I wish to question. It is clear that Hume thinks that (i) Locke does, in fact, offer us a demonstration of the causal 1 David Hume, A Treatise of Human Nature, ed. by L.A. Selby-Bigge (Oxford, 1888), I, iii, 3, p. 78. 2 Ibid., pp. 78-79. •Hume thinks that intuitive and demonstrative certainty belong only to unalterable relations of ideas, viz., resemblance, proportion in quantity and number, degrees of any quality, and contrariety. The causal principle does not fit into any of these relations and is therefore neither intuitively nor demonstratively certain. 418 LOCKE, HUME, CAUSALITY 419 principle, and (ii) in this demonstration Locke begs the question . I submit that both of these claims are false. According to Hume'.s account, Locke negatively demonstrates 4 the causal principle by way of a reductio ad absurdum argument. In short, the denial of the causal principle entails the absurd, unacceptable consequence that nothing can cause an object's existence. As Hume says: Whatever is produc'd without any cause is produc'd by nothing, or in other words, has nothing for its cause. But nothing can never be a cause, no more than it can be something, or equal to two right angles. By the same intuition that we perceive nothing not to be equal to two right angles, or not to be something, we perceive, that it can never be a cause; and consequently must perceive, that every object has a real cause of its existence.5 Cast in simple modus tollens form, the demonstration says: I. If an object is produced without a cause, then it is produced by nothing 2. But nothing cannot be the cause of an object 3. Therefore, it is produced by a real (i.e., external) cause. Hume claims that this argument begs the question. To say, in the major premise, that if an object lacks a cause or productive principle, it is produced by nothing, assumes nothing to be its cause. The very point in question, however, is whether an object need have any cause. And so, as Hume says: 'Tis sufficient only to observe, that when we exclude all causes we really do exclude them, and neither suppose nothing nor the object itself to be the causes of the existence; and consequently can draw no argument from the absurdity of these suppositions to prove the absurdity of that exclusion.6 •I am using ' negative demonstration ' in this context in the same way Aristotle does in the Metaphysics. Although the law of contradiction is the most selfevident of all principles, Aristotle claims that it can be " negatively demonstrated " by drawing out the absurd consequences of its denial. For example, if one denies the law of contradiction, then all things become one and there are no differences between things. See...