The history of Physical Science appears to exhibit, periodically, a race between the acmulation of data and the ability of its codification (usually, a mathematical theory) to find a natural place (in the codifying scheme) for much of the empirical findings. If the codifying scheme is a mathematical theory, capable of interpolation and extrapolation, according to the rules of the particular branch of mathematics employed, the ablest handlers of the theory are frequently confronted with a situation in which mathematical computation alone does not suffice. In such a situation the introduction of symbols, whose interpretation is not direct and simple (from the point of view of the methodology whereby the data were procured) is resorted to. This symbol is usually involved in a mathematical relation by a species of reasoning, which may be somewhat unfamiliar and remote from customary habits of thought. It is generally accepted as physically valid, if the mathematical formulation which involves it can produce results which account for the mass of data uncovered by experimenters. As an example of such a procedure we may mention the case of the Schrödinger Ψ-symbol, a symbol which was involved in Schrödinger's famous matter wave equation. The successes which such a theory enjoyed, particularly, in its initial stages, in formally relating the relative positions and intensities of spectral lines, with the atomistic concepts of gross matter which were inferred from the data of macroscopic measurement, such as the atomic mass, the electronic charge, Planck quantum of action, etc.,—these successes, gave a certain physical dignity to the Ψ-function itself. This dignity was further enhanced by the disclosure, by Schrödinger, of four functions of the Ψ-symbol (and its complex conjugate) which held the same place in the “continuity equation” as the classical charge density and the three components of current density. The successes accompanying this discovery for spectroscopic problems, in particular, are well known to Physicists.

During the course of the last century it has grown increasingly clear that not all the issues with which an experimental science can be faced are experimental issues. If there were no other ground for this belief, history itself would force upon us some such conviction. For there are differences of opinion dividing men today that have divided men from the earliest times recorded, and in every one of the ages in between the self-same issue will have involved in dissension, not an occasional disputant here and there, but all the best thinkers in all the known sciences of their day. Yet at no time has either party to such strifes been in possession of facts ignored by the other; for had this been the case, the ignorant party must ere now have been driven from the field by force of the facts it ignored. It is fair to suppose that an issue which has come no nearer to solution as century after century added its contribution to the store of human knowledge, cannot depend for its decision on any information to be looked for from the centuries to come.

In considering this problem a distinction should first be made between its scientific and it philosophical aspects. The scientific problem is that of defining in exact understandable terms those conditions and factors (with their various types of combination and interplay) which make possible the synthesis of the living organism from the simpler elements of the non-living environment, and also its maintenance in the adult state as a fully developed and autonomous organic individual. The problem as thus stated is one to be approached by methods of observation and experiment, leading to verifiable results which are then expressed in systematic and intelligible form. The final statements or representations thus reached, the accepted scientific generalizations, inevitably take on a theoretical form, and as such are necessarily partial and abstract. Many of them, in fact, are to be regarded primarily as simplifications or models devised in the interest of clear representation or understanding. Their relation to concrete reality may range from attempts at exact portraiture to formulæ or diagrams having little more than heuristic significance. Any realistic philosophy of nature must always remember how incomplete and provisional are the theoretical conceptions of any natural science.

The extent to which Ernst Haeckel was hated and attacked by reactionary scientists, philosophers, litterateurs and preachers, is, as Lenin has pointed out in his “Materialism and Empirocriticism,” a measure of the success with which he originally expounded the results of natural science and drove them home to their logical conclusions in the interpretation of nature on a materialistic basis. Haeckel, in the days of his greatest mental vigor, made himself the spearhead of the scientific attack upon the then dominant forces of theology and obscurantism, showing fearlessly how revolutionary were the results of modern science, and particularly those concerned with evolution, in altering fundamentally man's outlook upon the world in which he lived and his own nature. It has become the mode among many intellectual circles in Western countries to refer slurringly both to the more technical scientific work and to the more general reasoning of Haeckel, as being crude and out of date; but this derogation has its origin in the despair of the teleologists and is not founded in the facts of modern scientific development. Certainly, so far as genetics is concerned, the most modern results are not merely in harmony with, but brilliantly confirmatory of, those main tenets of Haeckel's general interpretation of nature which involved him in the bitterest controversy. In addition they help to show the general soundness of his more technical zoological contributions. By contrast, Haeckel's deficiencies in the realm of social affairs stand out the more strongly, although his own materialism of natural science is a necessary basis for an adequate social materialism. We will not concern ourselves here, however, with Haeckel's own social theories, but only with those in the field of natural science; it was only in the latter field that he attained his real prominence.

All of Freud's more recent writings extol the virtues of the scientific method. “The Future of an Illusion” ends with the definite suggestion that religious instruction be taken from the list of topics taught every child and that in its place children be taught to interpret reality in terms of natural science. A similar theme runs through “Civilization and its Discontents”; if there be any hope for humanity, it lies in the scientific method. Finally, Freud's “New Introductory Lectures” ends with the following lines—lines which must be very reassuring to many admirers of Freud (and the present writer counts himself one of these) who have been somewhat discomfited by some of the recent highly speculative passages from his pen:

If there is an essential difference as suggested in a preceding article, between the natural sciences on the one hand and the social studies on the other, in the sense that man has the power to change, and has repeatedly changed, existing social organizations, whereas he has no such power over natural phenomena, the meaning of social science must in this respect at least differ substantially from that of natural science. Elsewhere the present writer has designated society an “artificial creation,” much as the automobile or a steel mill is, i.e. made by the artifice of man. The artificial automobile or steel mill is of course fabricated in the light of the natural laws of physical science. Its construction would be impossible without a knowledge of these laws. There are also certain natural laws and tendencies in human nature and animal behavior which must serve as a foundation for any scientifically fabricated society, i.e. constructed on the basis of observation and verification of these tendencies on the one hand and a rigorous use of theory and analysis on the other. In short, despite any essential difference, as suggested, between natural and social science, the scientific method is apparently just as applicable in the one field as in the other. There is still much confusion on this score. But before pursuing further the significance of the distinction, artificial versus natural, it will be well to have before us more of what opposing schools of methodological thought in the social studies have to offer.