Chapter 61

Motion is the actualization of potency as such. For example, the bronze is potentially a statue, because it can take on the form of the statue. Thus, the melting down, the molding, and the finishing, which are all motions, are an actualization of the metal which is potentially a statue. Consequently, motion will be considered in all the categories in which potency is considered. And in those in which potency is not considered, motion will not be considered either. Thus motion is considered in the categories of substance, quantity, quality, and place. In substance there is generation and destruction; in quantity there is increase and decrease; in quality, alteration; and in place, motion in a circle, which is called ‘circular, and motion in straight line, which is called ‘direct. There are, moreover, six kinds of direct motion: upward, downward, inward, outward, motion to the right, and motion to the left. And so with circular motion there are seven kinds of motion with respect to place.

Now, everything that is changed is changed either in itself, or in something within itself, or in something around itself. If this is in the thing itself, it will constitute generation and destruction. If, however, it is in something in the thing itself, this will either be in quantity, in which case it will constitute increase and decrease, or it will be in quality, in which case it will constitute alteration. And if it is in something around the thing, then it will constitute change in place, because place is neither the thing itself which is moved, nor is it anything in it; rather, it accompanies the things moved and is round about them.

Generation differs from destruction. This is because generation is the passing from non-being to being, for that comes into being, or is generated, which was not before. But with destruction it is just the reverse, for destruction is the change from being to non-being. And increase differs from decrease, because increase is the motion to a greater quantity, whereas decrease is that to a lesser. And again, there are opposite passions in alteration, as heat is opposed to cold and black to white. Thus, while destruction is opposed to generation, and increase to decrease, to alteration are opposed the corresponding opposite and rest. For cooling is opposed to heating and so is rest,