From a purely psychological point of view, the introduction of new hypotheses and of new terms would appear justified if it led to a system free of contradictions, and to predictions verifiable by experiment. But, to take the latter test first, analysts of the orthodox Freudian, Jungian, and Adlerian schools all achieve some therapeutical results which seem to confirm prediction by experiment, though the theories on which the predictions are based are sometimes diametrically opposed to each other. The reason for this, and for the indecisive nature of the purely psychological approach in general, is the metaphorical character of psychological terms like “repression,” “censor,” super-ego,” inferiority complex,” and so forth, and the tautologies to which their manipulation often leads.

Arthur Koestler, Insight and Outlook: An Inquiry into the Common Foundations of Science, Art, and Social Ethics, 1949, New York, p. ix