This is to be explained by the fact that a feeling which corresponds to a certain sensational quality is, as a rule, a component of a complex affective system, in which it belongs at the same time to various dimensions. Thus, the affective quality of a tone of given pitch belongs not only to the dimension of pitch-feelings, but also to that of feelings of intensity and finally to the different dimensions in the clang-qualities of tones may be arraigned. A tone of middle pitch and intensity may, lie in the indifference-zone so far as feelings of pitch and intensity are concerned, and yet have a very marked clang-feeling. The passage of affective elements through the indifference-zone can be directly observed only when care is taken to abstract from other accompanying affective elements. The cases most favorable for this observation are those in which the accompanying elements disappear entirely or almost entirely. Wherever such an indifference-zone appears without complication with other affective elements, we speak of the state as free from feelings, and of the sensations and ideas present in such a state, as indifferent.
2) Feelings of specific, and at the same time simple and irreducible, quality appear not only as the subjective complements of simple sensations, but also as the characteristic attendants of composite ideas or even complex ideational processes. Thus, there is a simple tonal feeling which varies with the pitch and intensity of tones, and also a feeling of harmony which, regarded as a feeling, is just as irreducible, but varies with the character of compound clangs. Still other feelings, which may in turn be of the most various kinds, arise from melodious series of clangs. Here, again, each single feeling taken by itself at a given moment, appears as an irreducible unit. Simple feelings are, then, much more various and numerous than simple sensations.
3) The various pure sensations may be arranged in a number of separate system is, between whose elements there is no qualitative relation whatever.
Sensations belonging to different systems are called disparate. Thus, a tone and a color, a sensation of hot and one of pressure, or, in general, any two sensations between which there are no intermediate qualities, are disparate. According to this criterion, each of the four special senses (smell, taste, hearing, and sight) has a closed, complex sensational system, disparate from the other senses; while the general sense (touch) contains four homogeneous sensational systems (sensations of pressure, hot, cold, and pain). All simple feelings, on the contrary, form a single interconnected manifold, for there is no feeling from which it is not possible to pass to any other through intermediate forms or through indifference-zones.
But here too we may distinguish certain systems whose elements are more closely related, as, for example, feelings from colors, tones, harmonies, and rhythms. Still, they are not absolutely closed systems, but there are everywhere relations either of likeness or of opposition to other systems.
Thus, such feelings as those from sensations of moderate warmth, from tonal harmony, and from satisfied expectation, however great their qualitative differences may be, are all related in that they belong to the general class of "pleasurable feelings". Still closer relations xist between certain single affective systems, as, for example, between tonal feelings and color-feelings, where deep tones seem to be related to dark colors, and bright colors to high tones. When in such cases a certain relationship is ascribed to the sensations themselves, it is probably due entirely to a confusion of the accompanying feelings with the sensations.
This third distinguishing characteristic shows conclusively that the origin of the feelings is more unitary than that of the sensations, which depend on a number of different and in part distinguishable conditions.