A New Look at Hume's Theory of Probabilistic Inference

Hume Studies Volume 31, Number 1, April 2005, pp. 21-36 A New Look at Hume's Theory of Probabilistic Inference mark collier 1. Hume's Theory of Probabilistic Inference Historians of philosophy do not usually take Hume's theory of probabilistic inference seriously. For some scholars, Hume's account is dismissed because of its misguided reliance upon psychological rather than logical methods.1 Others are more sympathetic to Hume's naturalistic approach, but regard the specific proposals of his positive account as hopelessly naïve. If his contributions are to be judged as part of the empirical science of man ... then his 'results' will appear ludicrously inadequate, and there will be no reason to take him seriously.2 Still others are willing to defend many of Hume's positive proposals, but single out his account of probabilistic inference as "unsatisfactory"3 and "dubious."4 In this paper, I challenge these disparaging assessments. I argue that Hume's theory of probabilistic inference is neither misguided nor inadequate; quite the contrary, it stands at the leading edge of our contemporary science of the mind. Hume agrees with Leibniz that previous philosophers have been "too concise when they treat of probabilities" (T Abs.4;SBN647; cf. EHU6.4; SBN 59). In section 1.3.12 of the Treatise, he attempts to remedy this situation by laying out a theory of "conjectural or probable reasonings" (T 1.3.12.20; SBN 139). It is important to be Mark Collier is Assistant Professor of Philosophy, University of Minnesota, Morris, MN 56267 USA. e-mail: mcollier@morris.umn.edu 22 Mark Collier clear at the outset that Hume is interested primarily in a psychological rather than a metaphysical approach to probability. Hume does in fact subscribe to a particular metaphysical interpretation of probability, according to which it is nothing but a reflection of our ignorance concerning hidden causes, but this position is clearly of secondary interest and is not one that he defends at any length. His main concern is to explain how we manage to make predictive inferences under conditions of uncertainty, and for this issue, questions about the metaphysical nature of probability are idle; our philosophical interpretations of probability, he maintains, have no influence on how we carry out probabilistic inferences in our everyday lives. When causes are not followed by their usual effects, the vulgar take this as an indication of "contingency" in the cause, by virtue of which the same cause can sometimes produce different effects. In contrast, philosophers retain their commitment to the causal principle, and explain away putative counter-examples in terms of the "secret operation of contrary causes." The vulgar, who take things according to their first appearance, attribute the uncertainty of events to such an uncertainty in the causes, as makes them often fail of their usual influence, tho' they meet with no obstacle nor impediment in their operation. But philosophers observing, that almost in every part of nature there is contain'd a vast variety of springs and principles, which are hid, by reason of their minuteness and remoteness, find that 'tis at least possible the contrariety of events may not proceed from any contingency in the cause, but from the secret operation of contrary causes. (T 1.3.12.5; SBN 132) Nevertheless, philosophers who reject causal indeterminacy have no choice but to rely upon probabilities for guidance in their everyday lives. But however philosophers and the vulgar may differ in their explication of the contrariety of events, their inferences from it are always of the same kind, and founded on the same principles. (T 1.3.12.6; SBN132; cf. EHU 6.4; SBN 58) When philosophers make decisions or predictions under conditions of uncertainty, they must make probabilistic calculations just like the vulgar. Hume's primary concern in T1.3.12 involves the nature of our commonplace probabilistic inferences. What types of sensory perceptions lead us to make them? What degrees of belief do they generate? Which faculties of the mind enable us to draw such inferences? Hume regards these as empirical questions, and in order to make progress on them, he turns to the resources of his science of human nature . His...