23. For sense-objects, which receive their impulse from without, movement is a stimulus which agitates them, excites them, presses them, prevents them from slumbering in inertia, from remaining the same, and makes them present an image of life by their agitation and continual mutations. Besides, one must not confuse the things that move with movement; walking is not the feet, but an actualization of the power connected with the feet. Now as this power is invisible, we perceive only the agitation of the feet; we see that their present state is quite different from that in which they would have been, had they remained in place, and that they have some addition, which however, is invisible. Thus, being united to objects other than itself, the power is perceived only accidentally, because one notices that the feet change place, and do not rest. Likewise, alteration in the altered object, is recognized only by failure to discover in it the same quality as before.
MOVEMENT AS INFLUX.
What is the seat of a movement acting on an object by passing from internal power to actualization? Is it in the motor? How will that which is moved and which suffers be able to receive it? Is it in the movable element? Why does it not remain in the mover? Movement must therefore be considered as inseparable from the mover, although not exclusively; it must pass from the mover into the mobile (element) without ceasing to be connected with the mover, and it must pass from the mover to the moved like a breath (or influx).[426] When the motive power produces locomotion, it gives us an impulse and makes us change place ceaselessly; when it is calorific, it heats; when, meeting matter, it imparts thereto its natural organization, and produces increase; when it removes something from an object, this object decreases because it is capable thereof; last, when it is the generative power which enters into action, generation occurs; but if this generative power be weaker than the destructive power, there occurs destruction, not of what is already produced, but of what was in the process of production. Likewise, convalescence takes place as soon as the force capable of producing health acts and dominates; and sickness occurs, when the opposite power produces a contrary effect. Consequently, movement must be studied not only in the things in which it is produced, but also in those that produce it or transmit it. The property of movement consists therefore in being a movement endowed with some particular quality, or being something definite in a particular thing.
MOVEMENT OF DISPLACEMENT IS SINGLE.
24. As to movement of displacement, we may ask if ascending be the opposite of descending, in what the circular movement differs from the rectilinear movement, what difference obtains in throwing an object at the head or at the feet. The difference is not very clear, for in these cases the motive power is the same. Shall we say that there is one power which causes raising, and another that lowers, especially if these movements be natural, and if they be the result of lightness or heaviness? In both cases, there is something in common, namely, direction towards its natural place, so that the difference is derived from exterior circumstances. Indeed, in circular and rectilinear movement, if someone move the same object in turn circularly and in a straight line, what difference is there in the motive power? The difference could be derived only from the figure (or outward appearance) of the movement, unless it should be said that the circular movement is composite, that it is not a veritable movement, and that it does not produce any change by itself. In all of these cases, the movement of displacement is identical, and presents only adventitious differences.
EXPLANATION OF COMPOSITION AND DECOMPOSITION.
25. Of what do composition (blending, or mixture) and decomposition consist? Do they constitute other kinds of movement than those already noticed, generation and destruction, growth and decrease, movement of displacement and alteration? Shall composition and decomposition be reduced to some one of these kinds of motion, or shall we look at this process inversely? If composition consist in approximating one thing to another, and in joining them together; and if, on the other hand, decomposition consist in separating the things which were joined, we have here only two movements of displacement, a uniting, and a separating one. We should be able to reduce composition and decomposition to one of the above recognized kinds of motion, if we were to acknowledge that this composition was mingling,[427] combination, fusion, and union—a union which consists in two things uniting, and not in being already united. Indeed, composition includes first the movement of displacement, and then an alteration; just as, in increase, there was first the movement of displacement, and then movement in the kind of the quality.[428] Likewise, here there is first the movement of displacement, then the composition or decomposition, according as things approximate or separate.[429] Often also decomposition is accompanied or followed by a movement of displacement, but the things which separate undergo a modification different from the movement of displacement; similarly, composition is a modification which follows the movement of displacement, but which has a different nature.
COMPOSITION AND DECOMPOSITION ARE NOT ALTERATIONS.
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"?