more satisfaction to us if we can reduce them to quantitative order. Perhaps we shall have only partial success; but it may fairly be urged that psychology has done as much in this direction in fifty years as physics accomplished to the time of Galileo or chemistry to the time of Lavoisier.
The psychologist counts and he measures time, space and intensity. Even if it were true—I think it is not true—that mental magnitudes are not measurable, it would none the less be the case that mental processes are described in quantitative terms. This is attempted and accomplished in most of the researches published in our psychological journals. They describe measurements and the correlation of quantities; they show that a mental mechanics is more than a possibility.
The physical sciences have been primarily quantitative and the biological sciences are primarily genetic, but the physical sciences must become genetic and the biological sciences must become quantitative. Psychology is from the start both quantitative and genetic. It may indeed be claimed that it is the science in which the genetic method has the most complete application. Every mental state and every form of activity is the result of development from previous conditions. If explanation, as distinguished from description, is possible anywhere in science it is possible here. It is certainly difficult to penetrate by analogy into the consciousness of the lower animals, of savages and of children, but the study of their behavior has already yielded much and promises much more. Although those who make their psychology coterminous with introspection can not enter far into this field, they still have their own genetic problems. In whatever direction we turn the harvest is waiting; it is only the reapers who are few. Almost every observation, experiment or theory of organic evolution offers parallel problems for the psychologist. The development of the individual opens questions more numerous and more important for psychology than does the development of the body for other sciences. Senile, degenerative and pathological conditions are all there for psychological investigation. The evolution of society and the inter-relations of individuals are being gradually brought within the range of genetic psychology. It is quite possible that the chief scientific progress of the next fifty years will be in this direction.
The problems of psychology are certainly made endlessly complex by the fact that we have to do not with the development and condition of a single mind or individual, but with innumerable individuals. The traditional psychology has been disposed to ignore individual differences; but in attempting to prescribe conditions for all minds, it becomes schematic and somewhat barren. It is surely wasteful to select those uniformities that are true for all and to throw away those differences which are equally fit material for scientific treatment.
