Hume's Practical Skepticism: A Foundation for Probable Inquiry — Epoche B2
Hume's rules correct the custom they are supposed to describe The argument everyone agrees about David Hume's argument concerning inference from experience is not in dispute [1] , and it is worth stating exactly so that the disputed part can be isolated. All reasoning about matters of fact rests on the relation of cause and effect. Our knowledge of that relation comes from experience. But experience acquaints us only with past cases, and to move from these to a claim about the next case we need the assumption that the course of nature will continue uniform. That assumption is not demonstrable, since it implies no contradiction that nature should change; and it cannot be established from experience without using the very inference in question. Hume states the first half of this at Enquiry IV [2] , Part II, observing that no demonstrative argument is available because it implies no contradiction that an object seemingly like those we have experienced should be attended with different effects. So far, agreement. The dispute begins over what Hume takes himself to have shown, and this essay argues for one side of it. Hume's positive epistemology is normative: the rules he lays down are corrections of custom rather than reports of it, and his best-known applications of them are addressed against beliefs people actually and stably hold. The reading that makes his scepticism harmless by making it purely descriptive cannot accommodate this, and Hume's own resources for supplying the missing authority are of the wrong shape. A specialist can deny this, and the last two sections say how. The naturalist reading and its attractions Since Norman Kemp Smith's work in the 1940s [3] , and in a sharper form in Don Garrett's [4] , Hume has been read as a naturalist rather than a sceptic. On this reading the famous argument is not an attack on inductive belief but a piece of cognitive science: it identifies what does not produce the inference—reason, in the demonstrative sense—and then identifies what does. The identification comes at Enquiry V, Part I: Custom, then, is the great guide of human life. It is that principle alone which renders our experience useful to us, and makes us expect, for the future, a similar train of events with those which have appeared in the past. Read this way, no paralysis follows and none is threatened, because nothing was ever resting on reason to begin with. Hume is describing an animal that infers; he is not recommending that it stop. The reading is attractive because it fits Hume's stated method, the attempt to introduce the experimental method into moral subjects, and because it explains the cheerfulness of his conclusions. The rules, and what kind of thing they are The difficulty for that reading sits in a short section of the Treatise , 1.3.15, headed with rules by which to judge of causes and effects. Hume gives eight, and they fall into two groups. The first three restate his analysis of causation: cause and effect must be contiguous, the cause must be prior in time, and there must be a constant union between them. These are descriptive; they say what the relation consists in. The remaining five are of a different kind. The fourth lays down that the same cause always produces the same effect and the same effect never arises but from the same cause. The fifth says that where several different objects produce the same effect it must be by some quality they share, and directs us to find it. The sixth says that where two resembling objects have different effects, the difference must lie in the particular in which they differ. The seventh treats an effect that increases and diminishes with its cause as a compound of effects arising from the several parts of that cause. The eighth says that an object which exists for a time in full perfection without producing an effect is not the sole cause of it. Anyone who has met the canons of eliminative induction that John Stuart Mill later codified will recognise the fifth [5] , sixth and seventh. They are the methods of agreement, of difference and of concomitant variation, and they are instructions for finding something out. Why they are not descriptions Here is the argument this essay turns on. A description of custom would say what the mind does when it has been exposed to constant conjunctions. Hume's fifth rule does not say that. It says that when several different objects produce the same effect, we must look for the quality they have in common. Looking is an action. It requires selecting cases, holding factors fixed, and varying one thing at a time. No propensity performs these operations; propensities operate on the material presented to them, and the rules tell us to go and present different material. Hume is aware of this. He introduces them by observing that, since any thing may in principle produce any thing, we need general rules by which to know when objects really are causes and effects; and he closes the section by remarking that rules of this kind are very easy in their invention and extremely difficult in their application. Both sentences are about doing something well or badly. Custom does not err in the relevant sense; a propensity fires or it does not. Error, and its correction, belong to a level at which something can be done better or worse. Two more places where the normativity is undeniable The rules are not an isolated lapse. In Enquiry X, Part I, Hume writes that a wise man proportions his belief to the evidence, and builds on it a maxim about testimony to the miraculous: that no testimony suffices unless its falsehood would be more miraculous than the fact it reports. Neither sentence describes what minds do. The essay's whole target is a class of testimony that a great many minds accept, and it is offered in order that they should stop. And in Enquiry XII, Part 3, Hume recommends mitigated scepticism, or academical philosophy, as the position one should adopt, characterised by a limitation of inquiry to s