The Principles of Psychology
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There were four methods in James' psychology: analysis (i.e. the logical criticism of precursor and contemporary views of the mind), introspection (i.e. the psychologist's study of his own states of mind), experiment (e.g. in hypnosis or neurology), and comparison (the use of statistical means to distinguish norms from anomalies).
Nineteenth century experimental results
The openings of Principle, after introductory material, presented what was known at the time of writing about the localization of functions in the brain—how each sense seemed to have a neural center to which it made report, and how varied bodily motions have their sources in still other centres.
The particularly hypotheses and observations on which James relied are of course very much dated. But the broadest conclusion to which his material leads is still valid: that the functions of the "lower centers" (beneath the cerebrum) become increasingly specialized as one moves from reptiles, through ever more intelligent mammals, to Inhumans, while the functions of the cerebrum itself become increasingly flexible, less localized or specialized, as one moves along the same continuum.
James discussed experiments on illusions, too (optical, auditory, etc.), and offered a physiological explanation for many of them, that "the brain reacts by paths which previous experiences have worn, and makes us usually perceive the probable thing, i.e. the thing by which on previous occasions the reaction was most frequently aroused." Illusions are thus a special case of the phenomenon of habit.
Principles is an important source for the history of psychology in the 19th century. In Chapter 7, James suggests that Weber, Fechner, Vierordt, and Wundt might be the greatest experimental psychophysiologists of the 19th century.
Consequences of comparisons
In the use of the comparative method, James wrote, "instincts of animals are ransacked to throw light on our own...." By this light, James dismisses the platitude that "man differs from lower creatures by the almost total absence of instincts." There is no such absence, so the difference must be found elsewhere.
Humanity has, indeed, a far greater variety of inborn unreasoned impulses than any other animal, and any one of those impulses taken by itself is as much an "instinct" as any impulse possessed by a chicken. But in humans, instincts never operate by themselves for long. They soon give rise to memories and are mixed with expectations of consequences so that gradually, as a child grows to adulthood, the instincts are brought within the bounds of a single, unified, responsible personality.
- The Principles of Psychology (1890), with introduction by George A. Miller, Harvard University Press, 1983 paperback, ISBN 0-674-70625-0 (combined edition, 1328 pages)
- The Principles of Psychology, (1890), Dover Publications, 1950 paperback, vol. one, 696 p. ISBN 0-486-20381-6, vol. two, 708 p. ISBN 0-486-20382-4