[Sidenote] _Aesthetic activity and physical concepts._ Aesthetic activity is distinct from practical activity but when it expresses itself is always physical accompanied by practical activity. Hence its utilitarian or hedonistic side, and the pleasure and pain, which are, as it were, the practical echo of aesthetic values and disvalues, of the beautiful and of the ugly. But this practical side of the aesthetic activity has also, in its turn, a _physical_ or _psychophysical_ accompaniment, which consists of sounds, tones, movements, combinations of lines and colours, and so on. Does it _really_ possess this side, or does it only seem to possess it, as the result of the construction which we raise in physical science, and of the useful and arbitrary methods, which we have shown to be proper to the empirical and abstract sciences? Our reply cannot be doubtful, that is, it cannot be affirmative as to the first of the two hypotheses. However, it will be better to leave it at this point in suspense, for it is not at present necessary to prosecute this line of inquiry any further. The mention already made must suffice to prevent our having spoken of the physical element as of something objective and existing, for reasons of simplicity and adhesion to ordinary language, from leading to hasty conclusions as to the concepts and the connexion between spirit and nature. [Sidenote] _Expression in the aesthetic sense, and expression in the naturalistic sense._ It is important to make clear that as the existence of the hedonistic side in every spiritual activity has given rise to the confusion between the aesthetic activity and the useful or pleasurable, so the existence, or, better, the possibility of constructing this physical side, has generated the confusion between _aesthetic_ expression and expression _in the naturalistic sense_; between a spiritual fact, that is to say, and a mechanical and passive fact (not to say, between a concrete reality and an abstraction or fiction). In common speech, sometimes it is the words of the poet that are called _expressions_, the notes of the musician, or the figures of the painter; sometimes the blush which is wont to accompany the feeling of shame, the pallor resulting from fear, the grinding of the teeth proper to violent anger, the glittering of the eyes, and certain movements of the muscles of the mouth, which reveal cheerfulness. A certain degree of heat is also said to be the _expression_ of fever, as the falling of the barometer is of rain, and even that the height of the rate of exchange _expresses_ the discredit of the paper-money of a State, or social discontent the approach of a revolution. One can well imagine what sort of scientific results would be attained by allowing oneself to be governed by linguistic usage and placing in one sheaf facts so widely different. But there is, in fact, an abyss between a man who is the prey of anger with all its natural