Shall we have to admit that composition and decomposition are movements which exist by themselves, and analyze alteration into them? Condensation is explained as undergoing an alteration; that means, as becoming composite. On the other hand, rarefaction is also explained as undergoing an alteration, namely, that of decomposition; when, for instance, one mingles water and wine, each of these two things becomes other than it was, and it is the composition which has operated the alteration. We will answer that here composition and decomposition no doubt precede certain alterations, but these alterations are something different than compositions and decompositions. Other alterations (certainly) are not compositions and decompositions, for neither can condensation nor rarefaction be reduced to these movements, nor are they composed of them. Otherwise, it would be necessary to acknowledge the (existence of) emptiness. Besides, how could you explain blackness and whiteness, as being composed of composition and decomposition? This doctrine would destroy all colors and qualities, or at least, the greater part of them; for if all alteration, that means, all change of quality, consisted in a composition or decomposition, the result would not be the production of a quality, but an aggregation or disaggregation. How indeed could you explain the movements of teaching and studying by mere "composition"? MOVEMENTS DIVIDED IN NATURAL, ARTIFICIAL, AND VOLUNTARY. 26. Let us now examine the different kinds of movements. Shall we classify movements of displacement in movements upwards and downwards, rectilinear or curvilinear, or in movements of animate and inanimate beings? There is indeed a difference between the movement of inanimate beings, and that of animate beings; and these latter have different kinds of motion, such as walking, flying, and swimming. Their movements could also be analyzed in two other ways, according as it was conformable to, or against their nature; but this would not explain the outer differences of movements. Perhaps the movements themselves produce these differences, and do not exist without them; nevertheless, it is nature that seems to be the principle of the movements, and of their exterior differences. It would further be possible to classify movements as natural, artificial, and voluntary; of the natural, there are alteration and destruction; of the artificial, there are the building of houses, and construction of vessels; of the voluntary, there are meditation, learning, devoting oneself to political occupations, and, in general, speaking and acting. Last, we might, in growth, alteration and generation, distinguish the natural movement, and that contrary to nature; or even establish a classification founded on the nature of the subjects in which these movements occur. DISTINCTION BETWEEN STABILITY AND STILLNESS.