1. Two definitions of psychology have been the most prominent in the history of this science. According to one, psychology is the "science of mind", psychical processes being regarded as phenomena from. which it is possible to infer the nature of an underlying metaphysical mind­substance.
According to the other, psychology is the "science of inner experience"; psychical processes are here looked upon as belonging to a specific form of experience, which is readily distinguished by the fact that its contents are known through "introspection", or through the "inner sense" as it is called if one uses the phrase phrase which has been employed to distinguish introspection from sense-perception through the outer senses.
Neither of these definitions, however, is satisfactory to the psychology of today. The first or metaphysical definition belongs to a period of development that lasted longer in this science than in others. But is here, too, forever left behind, since psychology has developed into an empirical discipline, operating with methods of its own; and since the "mental sciences" have gained recognition as a great department of scientific investigation, distinct from the sphere the natural sciences, and requiring as a general groundwork an independent psychology, free from all metaphysical theories.
The second or empirical definition, which sees in psychology a "science of inner experience", is inadequate because it may give rise to the misunderstanding that psychology has to do with objects totally different from the objects of so called "outer experience". It is, indeed, true that there are certain contents of experience which belong in the sphere of psychological investigation, and are not to be found among the objects and processes studied by natural science; such are our feelings, emotions, and decisions. On the other hand, there is not a single natural phenomenon that may not, from a different point of view, become an object of psychology. A stone, a plant, a tone, a ray of light, are, when treated as natural phenomena, objects of mineralogy, botany, physics, etc. In so far, however, as they are at the same time ideas, they are objects of psychology, for psychology seeks to account for the genesis of these ideas, and for their relations, both to other ideas and to those psychical processes, such as feelings, volitions, etc., which are not referred to external objects. There is then, no such thing as an "inner sense" which can be regarded as an organ of introspection, and as distinct from the outer senses, or organs of objective perception. The ideas of which psychology seeks to investigate the attributes, are identical with those upon which natural science is based; while the subjective activities of feeling, emotion, and volition, which are neglected in natural science, are not known through special organs but are directly and inseparably connected with the ides referred to external objects.
2. It follows, then, that the expressions outer and inner experience do not indicate different objects, but different points of view from which we take up the consideration and scientific treatment of a unitary experience. We are naturally led to these points of view, because every concrete ex-]perience immediately divides into two factors: into a content presented to us, and our apprehension of this content .
We call the first of these factors objects of experience, the second, experiencing subject. This division indicates two directions for the treatment of experience. One is that of the natural sciences, which concern themselves with the objects of experience, thought of as independent of the subject. The other is that of psychology, which investigates the whole content of experience in its relations to the subject and also in regard to the attributes which this content derives directly from the subject. The point of view of natural science may, accordingly, be designated as that of mediate experience, since it is possible only after abstracting from the subjective factor present in all actual experience; the point of view of psychology, on the other hand, may be designated as that of immediate experience, since it purposely does away with this abstraction and all its consequences.
3. The assignment of this problem to psychology, making it a general, empirical science coordinate with the natural sciences, and supplementary to them, is justified by the method of all the mental sciences, for which psychology furnishes the basis. All of these sciences, philology, history and political and social science, have as their subject­matter, immediate experience as determined by the interaction of objects with knowing and acting subjects. None of the mental sciences employs the abstractions and hypothetical supplementary concepts of natural science; quite otherwise, they all accept ideas and the accompanying subjective activities as immediate reality. The effort is then made to explain the single components of this reality through their mutual interconnections. This method of psychological interpretation employed in each of the special mental sciences, must also be the mode of procedure in psychology itself, being the method required by the subject-matter of psychology, the immediate reality of experience.
