Psychology has a long past, yet its real history is short. For thousands of years it has existed and has been grow ing older; but in the earlier part of this period it cannot boast of any continuous progress toward a riper and richer development. In the fourth century before our era that giant thinker, Aristotle, built it up into an edifice compar ing very favorably with any other science of that time. But this edifice stood without undergoing any note worthy changes or extensions, well into the eighteenth or even the nineteenth century. Only in recent times do we find an advance, at first slow but later increasing in rapidity, in the development Of psychology. The general causes which checked the progress of this science and thus made it fall behind the others can readily be stated.