lives. Inert matter may be observed and measured more readily than the living body; physics consequently preceded biology in its development. The changes of mental life are more fleeting and obscure than those of the body. It is natural, therefore, that, as biology is more backward than physics, so psychology should be more backward than biology. There was a time when all the sciences were nourished by philosophy. In Greece the philosopher and the man of science were identical, and those who most advanced mathematics and science in the revival of learning are called philosophers. With the increase of knowledge division of labor became necessary, and the separate sciences were defined. Those sciences were first developed which found data ready in the common knowledge of daily life, and which embraced subjects where experiment and measurement could be most readily used. The close relation in which psychology still stands to philosophy is thus explained by its comparative backwardness. This relation is not essentially different from that of the other sciences. Philosophy is not the arithmetical sum of the special sciences, but has a peculiar task. It seeks to investigate the conditions of knowledge, and to form a theory of the ultimate nature and meaning of things. Psychology is no more concerned with these matters than is physics. Experimental and mathematical physics need not and should not investigate the origin and ultimate nature of matter, nor should psychology as a natural science concern itself with the origin, destiny, and meaning of mind. The subject-matter of psychology corresponds exactly to that of any other natural science. As physiology studies the phenomena of the living body, so psychology studies the phenomena of mind. It is often urged as an objection to psychology that the student can observe one mind only, but it is equally true that the student of physics can observe with one mind only. Were mental processes so irregular and idiosyncratic as is sometimes assumed, there would be no science of psychology, but physics would be equally out of the question. Psychology is not concerned with individual peculiarities, but with the laws to which all mental processes are subject. Its position is similar to that of physiology, which studies individual organisms in order to learn general truths concerning nutrition, movement, etc. The problems of psychology are evidently complicated by the fact that individual minds differ. But this difference is largely a matter of comparatively unimportant detail. The position of psychology is not very different from that of other sciences. Should astronomy seek to determine the orbits of all the satellites, of all the planets, of all the suns in the universe, it would have a hopeless task; but, if we understand one solar system, we have an astronomy to a large extent universal.
