Experimental psychology itself has, it is true, now and again suffered relapse into a metaphysical treatment of its problems.

From the standpoint of observation, then, we must regard it as a highly probable hypothesis that the beginnings of the mental life date from as far back as the beginnings of life at large.

Philosophical reflection could not leave the relation of mind and spirit in the obscurity which had satisfied the needs of the naive consciousness.

Physiology is concerned with all those phenomena of life that present them selves to us in sense perception as bodily processes, and accordingly form part of that total environment which we name the external world.

Physiological psychology is, therefore, first of all psychology.

The animal kingdom exhibits a series of mental developments which may be regarded as antecedents to the mental development of man, for the mental life of animals shows itself to be throughout, in its elements and in the general laws governing the combination of the elements, the same as the mental life of man.

The materialistic point of view in psychology can claim, at best, only the value of an heuristic hypothesis.