These facts—and we shall find analogous ones in other chapters, under other headings—show that, as we have seen in the case of pain, pleasure does not depend simply on the _quantity_ of excitement. To attribute all pleasures to excitements of medium energy is equivalent to the formula: “Pain is due to an intense and prolonged excitement.” In both cases intensity alone is emphasised; but there are pleasures irreducible to medium energy and depending on the _quality_ of the excitement and the nature of the sentient subject. Will it be said that sexual pleasures are the concomitants of a medium activity? The pleasure produced by harmonious chords is, for a musical ear, a matter of quality, not of intensity. We find it impossible, therefore, to reduce the objective conditions of pleasure to a single formula. Although general opinion has established a distinction between sensory and spiritual pleasures, this distinction is purely theoretical. Pleasure, as an affective state, always remains identical with itself; its numerous varieties are determined only by the intellectual condition originating it—sensation, image, concept. It would be tedious to repeat in detail the analysis already given of pain in order to apply it to pleasure; it will be sufficient to indicate the principal points. All forms of pleasure are accompanied by the organic modifications previously enumerated. Primarily, it can only be physical—_i.e._, combined with a sensation, such as the pleasure of a soft, warm contact, the satisfaction of hunger and thirst in children and animals. Then pleasure becomes an anticipation, as in the case of a dog when his food is being brought to him; to employ the term used by Herbert Spencer, it is a presentative-representative state. Then, in this ascending evolution, pleasure appears attached to pure representations. This—as in the case of pain—is the main group, that of the varied and numerous joys which console humanity for its sufferings; these, too, are divided into egoistic and sympathetic pleasures. There remain the highest and rarest manifestations attached to pure concepts—the pleasures of æsthetic creation, those of the metaphysician or the man of science. We might further show how the transition from pleasure, considered as strictly physical (that of the thirsty man drinking a cool beverage in long draughts), to the subtlest, most ethereal intellectual pleasures, may in fact be gradually traced step by step; that the two elements—sensory and representative—are always coexistent, and that we qualify any given pleasure solely according to the preponderance of one or the other. Finally, if we have found in hypochondriasis a composite form, which might be classed with equal justice as a physical or moral pain, in the domain of pleasure it is not difficult to discover analogous forms. The æsthetic pleasure called forth by forms, by colours, and especially by sounds, affords us an example. It is incontestable