Since natural science investigates the content of experience after abstracting from the experiencing subject, its problem is usually stated as that of acquiring "knowledge of the outer world". By the expression outer world is meant the sum total of all the objects presented in experience.
The problem of psychology has sometimes been correspondingly defined as "self knowledge of the subject". This definition is, however, inadequate, because the interaction of the subject with the outer world and with other similar subjects is just as much a part of the problem of psychology as are the attributes of the single subject. Furthermore, the expression can easily be interpreted to mean that the outer world and the subject are separate components of experience, or, at least, components which can be distinguished as independent contents of experience, whereas, in truth, outer experience is always connected with the apprehending and knowing functions of the subject, and inner experience always contains ideas from the outer world as indispensable components. This interconnection is the necessary result of the fact that in reality experience is not a mere juxtaposition of different elements, but a single organized whole which requires in each of its components the subject which apprehends the content, and the objects which are presented as content. For this reason natural science can not abstract from the knowing subject entirely, but only from those attributes of the subject which either disappear entirely when we remove the subject in thought, as, for example, the feelings, or from those attributes which must be regarded on the ground of physical researches as belonging to the subject, as, for example, the qualities of sensations. Psychology, on the contrary, has as its subject of treatment the total, content of, experience in its immediate character.
The only ground, then, for the division between natural, science on the one hand, and psychology and the mental sciences on the other, is to be found in the fact that all in the fact that all experience contains as its factors a content objectively presented, and an experiencing subject.
Still, it is by no means necessary that logical definitions of these two factors should precede the separation of the sciences from one another, for it is obvious that such definitions are possible only after they have a basis in the investigations of natural science and of psychology. All that it is necessary to presuppose from the first is the consciousness which accompanies all experience, that in this experience objects are being presented to a subject. There can be no assumption knowledge of the conditions upon which the distinction is based, or of the definite characteristics by which one factor is to be distinguished from the other. Even the use of the terms object and subject in this connection must be regarded as the application to the first stage of experience, of distinctions which are reached only through developed logical reflection.
The forms of interpretation in natural science and psychology are supplementary, not only in the sense that the first considers objects after abstracting, as far as possible, from the subject, while the second has to do with the part which the subject plays in the rise of experience; but they are also supplementary in the sense that each takes a different point of view in considering any single content of experience. Natural science seeks to discover the nature of objects without reference to the subject. The knowledge that it produces is therefore mediate or conceptual . In place of the immediate objects of experience, it sets concepts gained from these objects by abstracting from the subjective components of our ideas. This abstraction makes it necessary continually to supplement reality with hypothetical elements. Scientific analysis shows that many components of experience -- as, for example, sensations - are subjective effects of objective processes. These objective processes in their objective character, independent of the subject, can therefore never be a part of experience. Science makes up for this lack of direct contact with the objective processes, by forming supplementary hypothetical concepts of the objective properties of matter.
Psychology, on the other hand, investigates the contents of experience in their complete and actual form, both the ideas that are referred to objects, and also the subjective processes which cluster about these ideas.
The knowledge thus gained in psychology is, therefore, immediate and perceptual, -- perceptual in the broad sense of the term in which, not only senseperceptions, but all concrete reality is distinguished from all that is abstract and conceptual in thought. Psychology can exhibit the interconnection of the contents of experience, as these interconnections are actually presented to the subject, only by avoiding entirely the abstractions and supplementary concepts of natural science.
Thus, while natural science and psychology are both empirical sciences in the sense that they aim to explain the contents of experience, though from different points of view, it is obvious that, in consequence of the special character of its problem, psychology must be recognized as the more strictly empirical .