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 FBIEDRICH JODL, Lehrbiich der Psychologic. 235 reference to the aid which each furnishes or may be expected to furnish to the development of the science. Introspection, of course, stands first, its importance being neither too meanly esti- mated, nor too highly. A prominent place is given among the other methods to experimental hypnotism, which is regarded as far superior to " the occasional and mostly rather monotonous observations of psycho-pathology proper'' and as an important djunct to experimental normal psychology. This estimate rests on the assumption that hypnotism enables us to bring any feeling, idea, etc., at pleasure into the centre of the conscious process and to trace its influence. The subject of hypnotism is referred to in several subsequent passages, always, however, with stern exclu- sion of any suggestion of mysticism". It is held, for example, that the admission of telepathy would split the very foundations of all our science and lead to a thorough revision of our fundamental conceptions (p. 125). Much aid is also expected from the study of language, but little, on the other hand, from comparative or sociological psychology. As to physiological psychology, the ap- plication of this method to the entire realm of psychological ex- perience is held to be at present a scientific Utopia, though the ideal postulate is that we point out for every psychical pheno- menon a physiological correlate, and at the same time exhibit the unbroken continuity of the causal series of the neural processes. The hypothesis implied in this postulate is developed at length in the discussion of the following section on soul and body. The position adopted is that of a thorough-going parallelism in that form of the doctrine which declares that the two series, physio- logical and psychological, are " two aspects or two different modes of manifestation of one and the same process " (p. 57), " the same content expressed in two different languages " (p. 74). We are surprised to learn that this to us so familiar hypothesis has hither- to found but few friends in Germany (p. 75). Jodl rejects any application of it where the fact of consciousness is not plainly apparent. Many physiological processes have no psychical as- pect. I venture to think that this so popular double-aspect doctrine holds its position to-day by a somewhat uncertain tenure. Only the ambiguity of the facts can account for the diversity of intelli- gent opinion on the subject. No one probably denies that there is interdependence of some sort between the mental and the bodily series, and the most obvious reading of the facts would seem to make this interdependence mutual. That physiological process influences, i.e., is a condition of the coming to pass of the psychological process, is admitted, and, apart from methodologi- cal considerations, no one probably would hesitate to accept the converse proposition that psychological process influences, in the same sense, physiological process. In common parlance, the body affects the mind and the mind affects the body. Such interdepen- dence of process bears but a faint analogy to the dependent varia-