The need for a fundamental elaboration of the concepts of the general science—this algebra of the particular sciences—and its role for the particular sciences is even more obvious when we borrow from the area of other sciences. Here, on the one hand, it would seem that we have the best conditions for transferring results from one science into the system of another one, because the reliability, clarity and the degree to which the borrowed thesis or law have been fundamentally elaborated are usually much higher than in the cases we have described. We may, for example, introduce into the system of psychological explanation a law established in physiology or embryology, a biological principle, an anatomical hypothesis, an ethnological example, a historical classification etc. The theses and constructions of these highly developed, firmly grounded sciences are, of course, methodologically elaborated in an infinitely more precise way than the theses of a psychological school which by means of newly created and not yet systematized concepts is developing completely new areas (for example, Freud’s school, which does not yet know itself). In this case we borrow a more elaborated product, we operate with better-defined, exact, and clear unities; the danger of error has diminished, the likelihood of success has increased.

On the other hand, as the borrowing here comes from other sciences, the material turns out to be more foreign, methodologically heterogeneous, and the conditions for appropriating it become more difficult. This fact, that the conditions are both easier and more difficult compared with what we examined above, provides us with an essential method of variation in theoretical analysis which takes the place of real variation in the experiment.

Let us dwell upon a fact which at first sight seems highly paradoxical and which is therefore very suitable for analysis. Reflexology, which in all areas finds such wonderful coincidences of its data with the data of subjective analysis and which wishes to build its system on the foundation of the exact natural sciences, is, very surprisingly, forced to protest precisely against the transfer of natural scientific laws into psychology.

After studying the method of genetic reflexology, Shchelovanov15—with an indisputable thoroughness quite unexpected for his school—rejected the imitation of the natural sciences in the form of a transfer of its basic methods into subjective psychology. Their application in the natural sciences has produced tremendous results, but they are of little value for the elaboration of the problems of subjective psychology.* Herbart and Fechner16 mechanically transferred mathematical analysis and Wundt the physiological experiment into psychology. Preyer’7 raised the problem of psychogenesis by analogy with biology and then Hall and others borrowed the MUller-Haeckel principle from biology and applied it in an uncontrolled way not only as a methodological principle, but also as a principle for the explanation of the “mental development” of the child. It would seem, says the author, that we cannot object to the application of well-tried and fruitful methods. But their use is only possible when the problem is correctly stated and the method corresponds to the nature of the object under study. Otherwise one only gets the illusion of