Time, space and matter are the most pervasive and inescapable aspects of the physical universe. And yet, notwithstanding the fact that they represent the most fundamental and ubiquitous characteristics of reality, they have always presented elements of mystery to the human mind. Thus on the level of common thought we ponder how the withering hand of time reaches from out the past into the future to bring decay and destruction to all things; and on the more sophisticated level, after the fashion of Immanuel Kant, we are puzzled by certain antinomies of thought concerning the necessity for an origin, and an end, of the universe in time and space, in the face of the equally necessary reasons for regarding the universe as being unlimited in its space and time dimensions. In either case, however, we are paying tribute to the tantalizing nature of these problems concerning the cosmic framework of space-time-matter in which we live, and move, and have our being. Indeed, it is not too much to say that genuine philosophy took its origin in Zeno's paradoxes of motion, and will have its final consummation when it solves Kant's antinomies.

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.

One of the interesting and encouraging signs of our times is the fact that the several sciences are learning to develop and carry their own philosophy. Here psychology seems to me to be a bit backward. In this paper I am presuming to suggest that the time has come when the psychologist should take over the subject of theory of knowledge, emancipate it from the leading-strings of Mother Philosophy, and make it a phase of his own science and of its organizing and interpretative philosophy. In fact, I am suggesting that thinking and knowing of whatever sort, even psychologizing and philosophizing, being matters of “mental” activity, are properly object matters for the psychologist, when he really knows his stuff; and I am presuming to say that he is now well enough advanced towards this goal so that he should accept this implied challenge and proceed to take possession of this most significant portion of his proper field. This should greatly enlarge the field of psychological experimentation; it should open up new areas, that are even more significant for our science than are animal psychology and the psychology of learning, as we have hitherto envisioned these; and it should result in a development of principles for the better organization of our findings in these fields.

Reference to quantum theory has become quite the fashion, and to base an expectation on an already receding episode with relativity theory, a great philosophical assault of interpretation of quanta is brewing in many quarters. The author of this series of studies would be content if by a plain statement of “what is the case” at this stage he could stem the more quixotic efforts, or rather reveal their unreal character to the spectators who may be enmeshed in the spell cast over such adventures. It is constantly necessary to restate the physicists' claims plainly in their positive content—as Einstein himself did once for relativity theory—so that one may know what is no-man's land and what is everyman's land in the new territory. This in itself is largely but a hope since there is no unanimity as to all the facts, and, worse, unanimity is no guarantee of stability. Nevertheless, the painstaking revision that is constantly going on on the experimental front enables us to arrange at least the data on a well-ordered scale of reliability. It then becomes much easier to detect false props to otherwise attractive theories, to discriminate live matter from the débris of progress, and to speculate on future growth. For such reasons the present examination of the various quantum theories will proceed from a presentation of facts and theories to their appraisal and then to a proposal concerning the organization of the facts, concepts and theories. The subject is very complex: There are several quantum theories, some of which are already referred to as “classical” although these themselves were anti-classical (anti-Newtonian); all have claimed success in their time; all have serious hiatuses, including the present. The author has chosen to hark back to some of the older issues before appraising the latest claims.

The extent to which the scientific method has yielded to analysis in recent years serves only to emphasize by contrast the presence within that method of an irrational element. For it is becoming increasingly evident that whatever one may say of the logical and psychological character of the pre-inductive operations, of the formal processes involved in deducing the consequences of a given theory, of the technique of experimental corroboration, and of certain other aspects of the scientific method, there is one phase of the movement which remains a surd. This is the act of the creative imagination through which hypotheses and theories are called into being. Its mysterious character is exhibited in the terminology which is employed in describing it, in the variety and inconstancy of the conditions which give rise to it, in the apparent impossibility of controlling it, and in the impossibility of recognizing completely the adequacy of its results when it does occur. It is variously described as an act of intuition, mystic revelation, divine insight, a flash of understanding; it arises out of the greatest variety of conditions: acute and prolonged attention to the data in the confinement of the laboratory, or the complete relaxation of a walk in the country, or the intense mental effort upon a problem in a wholly unrelated field; it forbids direction, in fact it seems to arise most readily when the element of effort and control is conspicuously absent; it cannot even be certainly identified, for many supposed acts of discovery prove later to have produced only groundless fancies and absurd creations of the unguided imagination.

Biologists have as yet taken but little cognizance of the revolution in human thought which has been inaugurated by physicists in the last five years, and philosophers have stressed its negative rather than its positive side.

The historical origin and the experimental basis of the concept of physical determinism indicate that this basis was removed with the acceptance of the kinetic theory of matter, while its difficulties are increased by the admission that human nature, in its entirety, is a product of natural causation. An indeterministic view of causation has the advantages (a) of unifying the concept of natural law in different spheres of human experience and (b) of a greater generality, which precludes the acceptance of the special case of completely deterministic causation, so long as this is an unproved assumption. It is not inconsistent with the orderliness of the world, or with the fruitful pursuit of natural knowledge. It enriches rather than weakens the concept of of causation. It possesses definite advantages with respect to the one-sidedness of human memory, and to the phenomena of aiming and striving observable in man and other animals. Among biological theories it appears to be most completely in harmony with the theory of natural selection, which in its statistical nature resembles the second law of thermo-dynamics.

In an indeterministic world natural causation has a creative element, and science is interested in locating the original causes of effects of special interest, and not merely in pushing a chain of causation backwards ad infinitum. These contrasting tendencies are illustrated by a critique of the mutation theory, and by an attempt more closely to define the sense in which indeterministic causation should be thought of as creative.