Story of Psychology - Morton Hunt [53]
Hume’s main purpose in writing the Treatise was to develop a moral philosophy based on “the science of man,” meaning psychology. He therefore undertook to construct a theory of the human passions and our ideas of them, and this necessitated his knowing where our ideas come from. He approached the matter as a true empiricist: “As the science of man is the only solid foundation for the other sciences, so the only solid foundation we can give to this science itself must be laid on experience and observation.”43
Accordingly, while he made ample and critical use of the work of others, he relied in considerable part on introspective observation of his own mind. As a thoroughgoing empiricist, he peremptorily dismissed all questions about the nature of the incorporeal soul—the thinking “I” that had seemed so significant to Descartes—declaring that the nature of soul was an “unintelligible question” not even worth discussing. His own view of the conscious thinking self, based on a scrutiny of his own thought processes, was that the mind was made up entirely of perceptions:
When I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure…I may venture to affirm the same of the rest of mankind, that they are nothing but a bundle or collection of different perceptions.44
Hume distinguished between “impressions” (his word for sensations or perceptions) and “ideas” (the same experiences, but in the absence of the object, as in memories, reflections, and dreams). Like Locke, he said that these simple elements are the components of which complex and abstract ideas are formed. But how? Here he went far beyond Locke. There must be a “uniting principle,” which, he hypothesized, takes three forms: “The qualities, from which this association arises, and by which the mind is, after this manner, conveyed from one idea to another, are three, viz. resemblance, contiguity in time and place, and cause and effect. ”45
The association or combining of ideas by means of these three characteristics seemed to Hume the fundamental principle of the mind and as central to its operations as gravitation to the motions of the stars; he even called association “a kind of attraction” that causes ideas to cohere. He thus made much more of association than had Locke, who relied on it chiefly to explain abnormal connections among ideas but not mental processes in general.
So far, so good. But Hume, though convinced that he had found the fundamental scientific law of the mind, proceeded to undercut the very foundation of the sciences by his interpretation of one of the three forces of association, namely, cause and effect. He did not, as is sometimes claimed, say there is no such thing as cause and effect; he did say, however, that we cannot experience causality directly and therefore cannot know what it is or even prove that it exists. We know only that certain events seem always, or almost always, to be followed by certain others, and we therefore infer that the first causes the second. But this is only expectation based on the association of the two events:
The idea of cause and effect is derived from experience, which informs us that such particular objects, in all past instances, have been constantly conjoined with each other… All our reasonings concerning causes and effects are derived from nothing but custom.46
Causality is only a habit of mind. We do not and cannot experience or perceive it in any fundamental sense; we know only that when one thing happens, the other happens. To predict that this will always be so is to commit a fallacy; we can only infer that when A next occurs, B will probably follow.
Hume concluded that we believe in causality and in the reality of the external world not because we really know that they exist