factors are necessary--the subject who knows and the object thought about, independent of this subject. The investigation of the subject in his characteristics, as revealed to us in human consciousness, forms therefore not only a necessary supplement to the investigations of natural science, but it also attains to a more universal importance, since all mental values and their development arise from immediately experienced processes of consciousness, and therefore can alone be understood by means of these processes. And this is exactly what we mean by the principle of the actuality of mind.