An Enquiry Concerning Human Understanding | Study Guide

David Hume

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An Enquiry Concerning Human Understanding | Section 5 : Skeptical Solution of These Doubts | Summary



Part 1

The idea of causation is not derived in the ordinary way—from a sense impression. It is also not rationally justified—it is not justified either by relationships between ideas or matters of fact. In this section, Hume wants to provide an answer to the question, How do I have the idea of causation? By example, Hume sums up the results of his investigation thus far by asking the reader to imagine that a rational person were to suddenly appear on Earth. That person, he says, "would, indeed, immediately observe a continual succession of objects, and one event following another; but he would not be able to discover any thing farther."

The hypothetical man does find himself "determined to draw [inferences]" only after repeated similar experiences. Hume maintains the determination is explained by the principle of "custom or habit." It is, furthermore, a natural feature of human beings. "All inferences from experience, therefore, are effects of custom, not of reasoning."

This descriptive account does not, Hume thinks, render the idea of causation useless. Indeed, quite the contrary is the case. Being able to connect experiences by way of the principle of custom or habit is essential for navigating life. What Hume wants to make clear is that this principle yields belief rather than knowledge.

Part 2

Having isolated belief as the quality of certain kinds of ideas, Hume proceeds in this part of Section 5 to investigate its source and nature. According to Hume, beliefs are ideas felt in specific ways. It is its peculiar feeling that distinguishes beliefs from fictitious products of the imagination. Whereas "some sentiment or feeling" is "annexed" to belief, it is not so connected to products of the imagination.

This feeling "must be excited by nature, like all other sentiments." More specifically, the belief in causal relations is "excited" by particular situations, that is, by a memory or sensation. In short, belief is a feeling or sentiment. Hume defines belief, then, as "a more vivid, lively, forcible, firm, steady conception of an object, than what the imagination alone is ever able to attain." Insofar as the "manner" of conceiving—the formation of a belief—is nonrational, belief is not under one's control. The feeling that is a belief is not willed but instead is simply a natural state.

The conditions for this natural state are the "customary conjunction of the object with something present to the memory or senses." When presented with a memory or a sensation, one's attention is "carried" to a correlated idea, which is not present. Hume here returns to the principles of association first presented in Section 2: resemblance, contiguity, and cause and effect.


The title of this section, "Skeptical Solution of These Doubts" contains, in a nutshell, Hume's fundamental position on knowledge of causal claims. He does not think knowledge of causation is possible. It is important to remember that Hume takes the impression of the senses as the criterion of knowledge. Consequently, any legitimate idea or knowledge claim is traceable to an original impression. Causal judgments connect two entirely discrete impressions or make a predictive connection between one existing impression and one that is anticipated. In either case, this connection is not itself an impression. For example, the sight of the sun rising is connected with the prediction of the anticipated rise tomorrow; the sound of barking is connected with an unseen dog.

Moreover, Hume has argued that this connection is not justified by reasonings among relations of ideas or between matters of fact. Consequently, causal judgments are not only untraceable in the normal way, they are also not logically justified. This is what makes Hume a skeptic about knowledge claims concerning causation. What makes his solution skeptical is the fact that he does not rely on reason (human rationality) for that solution. Instead, psychological states account for belief in causal relations between objects and events.

To claim that one event causes another event—fire causes heat—is to claim that one believes that experience of one will be closely followed by or will be simultaneously experienced with the other. Similarly, to claim that one object causes an effect in another object—one billiard ball causes a second to move—is to reflect an anticipation of the second ball's movement upon being hit by the first.

Hume describes the psychological states in terms of mental "custom," "habit," "anticipation," and "propensity." These states arise from the "constant conjunction" of objects and events. Habits are the result of mechanical associations, so that expectations and anticipations are nothing other than conditioning. "Custom, then," Hume asserts, "is the great guide of human life." It is by way of one's becoming accustomed to things being a certain way that one makes the sorts of judgments that, as Hume has pointed out earlier in the section, allow one to "go beyond the evidence of our memory and senses." It is an instinctive sort of principle, not a product of rationality. It is for this reason that Hume refers to causal ideas as beliefs, not knowledge.

A belief is the result of "an operation of the soul," by which Hume means an operation of the mind. This is not, however, the same as a logical operation, which he has already sought to prove. Instead, it is a psychological operation, "as unavoidable as to feel the passion of love, when we receive benefits; or hatred, when we meet with injuries." As Hume points out, this sort of response, the belief, is the result of operations taken to be "a species of natural instincts," not rational operations like relations of ideas and matters of fact.

Why should Hume begin a discussion of belief by contrasting belief with fictions? Does he think that the imagination is the faculty that produces beliefs but that these products are different from, for example, golden mountains and satyrs? Hume claims, "Nothing is more free than the imagination of man," which is limited only by its source, namely experience. Perhaps its nature as a creative capacity accounts for the belief that objects and events are causally related.

Hume likely focuses on imagination as the possible source of belief because of this creative power. As he points out, however, one can imagine a man's head on a horse's body, but one cannot believe such creatures exist. Fictions, therefore, are connected with will in a way that belief is not. Instead, the connection is between belief and feeling or sentiment. More precisely, Hume asserts, belief just is a feeling. The idea of causation is a belief formed through experience, though it is not derived from it.

In this part of Section 5, Hume is not interested in arguing whether or not beliefs are justified. Instead, he argues for a particular description of their nature and formation. In so doing, he "distinguishes the ideas of judgment from the fictions of the imagination." In other words, judgments and fictions are the results of rational actions. These may indeed provide the materials for belief, but they are not equivalent to it.

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