An Enquiry Concerning Human Understanding | Study Guide

David Hume

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An Enquiry Concerning Human Understanding | Summary



Section 1: Of the Different Species of Philosophy

Hume is interested in developing "the science of human nature." He begins the book by distinguishing two approaches to that science. One involves philosophical thinking appropriate "to the entertainment, instruction, and reformation of mankind." It reflects a view of man as primarily "born for action." The second approach involves philosophical thinking appropriate to cultivating understanding. This approach reflects a view of man as "a reasonable rather than an active being ... a subject of speculation."

Human beings are not entirely actors and not entirely thinkers. Instead, they are both. Nevertheless, and more precisely, the approach Hume favors is one that will explain human nature, regardless of its relative unpopularity. This, he thinks, is provided by empirical philosophy guided by the scientific method.

Section 2: Of the Origin of Ideas

Hume asserts that all knowledge is derived from sense impressions. These are experiences gathered by the senses. Ideas are copies of these. To the extent that ideas are derived from impressions, they are less vivid and forceful than the original sense impression. As Hume writes, "The most lively thought is still inferior to the dullest sensation."

Whether internal or external, an impression makes an idea possible. "Inward" impressions include the emotions, such as love and hate, while "outward" impressions consist of those involving an organ of sense. Consequently, if one wants to determine the legitimacy of an idea, one need only trace it to an original impression.

Section 3: Of the Association of Ideas

The mind naturally organizes ideas by way of their associations, what Hume calls "a principle of connection." They are resemblance, contiguity, and cause and effect. One associates an idea with another one by the principle of resemblance, where the first idea resembles the second, as happens with a portrait that looks like the actual person. Another way in which one associates ideas enlists the principle of contiguity. One idea is contiguous with another when the two share elements, as two adjacent apartments share a wall. Lastly, the principle of cause and effect explains how one idea prompts the thought of another, as a wound prompts the idea of pain.

Section 4: Skeptical Doubts Concerning the Operations of the Understanding

Human reason proceeds experientially and nonexperientially. Hume calls experiential reasoning "Matters of Fact" and nonexperiential reasoning" Relations of Ideas". The negation of a statement that results in a contradiction demonstrates a statement of relations of ideas. So, for example, the proposition, "A square is not a four-sided figure" is contradictory, and so it is a statement of relations of ideas. The negation of a statement of a matter of fact, however, can never be contradictory. For example, "This room does not have four walls" is not contradictory; the room could have three walls.

Hume presents another criterion for classifying statements as relations of ideas or matters of fact. Here, the standard is epistemological. In other words, one knows a statement by way of the relations of ideas if, by reason alone, its truth is guaranteed. The meanings of square and four-sided figure are sufficient to know that the statement "A square is a four-sided figure" is true.

Matters of fact, on the other hand, cannot be known a priorithat is, by pure reason, or what Hume calls "the mere operation of thought." The truth of such statements can't be guaranteed but is instead only probable. Moreover, any statement of a matter of fact reflects a causal, or inductive, inference. This sort of inference goes beyond immediacy of sense impressions, as when, for example, one predicts the sun will rise tomorrow. Hume now turns his attention to a question that emerges from this fact: How does one know that the inference is correct? After all, the legitimacy of any statement depends on its grounding in experience or the memory of experience, and there does not appear to be any impression of causation.

There are only two ways to logically justify a causal claim: relations of ideas or matters of fact. Since causal claims are experiential, relations of ideas cannot justify a causal inference. That leaves matters of fact, but as Hume points out, precisely because matters of fact inferences are just causal inferences, to cite the former as a justification for the latter is to engage in circular reasoning.

Section 5: Skeptical Solution of These Doubts

Since there is no rational justification for causal inferences—neither relations of ideas nor matters of fact can do the job—Hume concludes that the inference is the result of "custom or habit." Hume asserts that the "constant conjunction of two objects, heat and flame, for instance," generates a propensity of the mind to expect the one whenever the other is presented. In short, it is not by any rational inference that the idea of a causal connection links one event with another, but simply a psychological habit. Custom—"that great guide of human life"—is a principle of the mind that explains the causal association of ideas, which, in turn, are the bedrock of all experiential reasoning.

Section 6: Of Probability

Probability judgments express a level of confidence about a future event. Just because he denies knowledge of causation, Hume does not think that things happen by chance. Probability, he argues, "arises from a superiority of chances on any side." It is the mind that weighs up these chances, with belief emerging as the probability increases. Consequently, belief that the sun will rise tomorrow correlates with the degree of probability that it will.

Section 7: Of the Idea of Necessary Connection

Metaphysical arguments typically involve ideas such as "power, force, energy, or necessary connection." These, Hume claims, are "obscure and uncertain." In other words, arguments that include these ideas assume that causes contain within themselves that which is efficacious. Consequently, the relation between cause and effect is thought to be a necessary connection. Hume's response is that the understanding is no more knowledgeable about this connection than it is about the idea of causation itself.

Section 8: Of Liberty and Necessity

Hume applies his theory of necessary connection to human action. Just as natural events occur according to laws, even if one cannot discern their operations, so also human actions are governed by natural laws. Humans' motives are not necessarily connected to their actions, but, Hume argues, they are constantly conjoined. Given that constant conjunction of events is Hume's definition of causation, human actions can be said to be caused by motives.

Section 9: Of the Reason of Animals

Human and nonhuman animals share a variety of features, such as the capacity for sensory and emotional experiences and the ability to learn and make inferences. Rather than consider human and nonhuman animals as radically different in their capacities, Hume claims differences in degree. So, while it is true that nonhuman animals do not have the sophisticated cognitive capacity apparently required to engage in morality and politics, for example, they do have many other similar experiences.

Section 10: Of Miracles

A miracle is a violation of a natural law. That violation is a divine intervention in the regular causal sequence of natural events. Hume argues that what people call miraculous is merely the violation of what they expect to occur. Moreover, since what people expect to occur—what they believe—is not actually natural law, it follows that the violation is not a transgression of natural law. Consequently, what people claim to be miracles are, in fact, not actually miracles. When someone reports a miracle, even when that person is otherwise a credible source, the evidence against miracles occurring outweighs that credibility.

Section 11: Of a Particular Providence and of a Future State

Western religious traditions include belief in a monotheistic divinity who intervenes in human affairs. Hume argues, in the guise of a "friend who loves skeptical paradoxes," that there is no evidence for such a belief. God does not, Hume asserts, control events such as death and floods.

Section 12: Of the Academical or Skeptical Philosophy

Hume concludes An Enquiry Concerning Human Understanding with a section on the origins of skepticism. It is the skeptical philosophical approach Hume enlists in the book, and this final section is a sustained examination of it. Two influential ancient skeptical groups, the Academics and the Pyrrhonians, present philosophical traits Hume admires. The Pyrrhonians, for example, hold that, since any plausible belief can be countered by an equally plausible opposite belief, one should suspend judgment. This view reflects suspiciousness of the intellectual capacity to judge beyond appearances, or what is perceived. While Hume does not agree that suspension of judgment is possible—it goes against human nature and does not lead to good practical outcomes—he does express admiration for the Pyrrhonists' implicit intellectual humility.

Academic skepticism emerged from Plato's university, the Academy. Academic skeptics followed the Socratic line of inquiry as the appropriate goal of philosophy, which values the pursuit of truth while maintaining that little is actually known. Hume takes this approach to be reflective of his own epistemological views. (Epistemological refers to the study of the nature and basis of human knowledge.) The skepticism of the Academics is "mitigated" by a commitment to critical inquiry.

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