1. The immediate contents of experience which constitute the subject-matter of psychology, are under all circumstances processes of a composite character.
Sense-perceptions of ex- ternal objects, memories of such sense-perceptions, feelings, emotions, and volitional acts, are not only continually united in the most various ways, but each of these processes is itself a more or less composite whole. The idea of an external body, for example, is made up of partial ideas of its parts. A tone may be ever so simple, but we localize it in some direction, thus bringing it into connection with the idea of external space, which is highly composite. A feeling or volition is referred to some sensation that aroused the feeling or to an object willed. In dealing with a complex fact of this kind, scientific investigation has three problems to be solved in succession. The first is the analysis of composite processes; the second is the demonstration of the combinations into which the elements discovered by analysis enter; the third is the investigation of the laws that are operative in the formation of such combinations.
2. The second, or synthetic, problem is made up of several partial problems. In the first place, the psychical elements unite to form composite psychical compounds which are separate and relatively independent of one another in the continual flow of psychical processes. Such compounds are, for example, ideas, whether referred directly to external impressions or objects, or interpreted by us as memories of impressions and objects perceived before. Other examples are composite feelings, emotions, or volitions.
Then again, these psychical compounds stand in the most various interconnections with one another. Thus, ideas unite to from larger simultaneous ideational complexes or regular successions, while affective and volitional processes form a variety of combinations with one another and with ideational processes.
In this way we have the interconnection of psychical compounds as a class of synthetical processes of the second degree, consisting of a union between the simpler combinations, or those of elements into psychical compounds. The separate psychical interconnections, in turn, unite to form still more comprehensive combinations, which also show a certain regularity in the arrangement of their components. In this way, combinations of a third degree arise which we designate by the general name psychical developments . They may be divided into developments of a different scope. Developments of a more limited sort are such as relate to a single mental trend, for example, the development of the intellectual functions, of the will, or of the feelings, or of merely one special branch of these functions, such as the aesthetic or moral feelings. From a number of such partial series arises the total development a psychical personality. Finally, since animals and in a still higher degree human individuals are in continual interrelation, with like beings, there arise above these individual forms the general psychical development s.
These various branches of the study of psychical development are in part the psychological foundations of other sciences, such as the theory of knowledge, aesthetics, and ethics, and are, accordingly, treated more appropriately in connection with these. In part they have become special psychological sciences, such as child-psychology, animal and social Psychology. We shall, therefore, in this treatise discuss only those results from the three last mentioned departments which are of the most importance for general psychology.
3. The solution of the last and most general psychological problem, the ascertation of the laws of psychical phenomena, depends upon the investigation of all the combination of different degrees, the combination of elements into compounds, of compounds into interconnections, and of interconnections into developments. And as this investigation is the only thing that can teach us the actual position of psychical processes, so we can discover the attributes of psychical causality, which finds its expression in these processes, only from the laws followed by the contents of experience and their components in their various combinations.
We have, accordingly, to consider in the following chapters:
1) Psychical Elements, 2) Psychical Compounds, 3) Interconnection of Psychical Compounds, 4) Psychical Developments, 5) Psychical Causality and its Laws.
