Definition of motion

One of the first times I thought I understood Aristotle’s definition of motion was when I saw it as a sort of middle state: potency as such is just an order to a term and so has the sense of a terminus a quo; and so the act of that potency is the very thing it is ordered to, the terminus ad quem. Motion is clearly between the two: the act of the potency as such.

Say there is a plane that shuttles daily from Memphis to Las Vegas. While on the ground in Vegas, you can call it the Memphis plane, regardless of what direction its pointed in or who’s on it. While in the air, however, it needs more than this to continue being the Memphis plane – it needs a definite direction and a pilot performing certain motions and thinking certain thoughts. But what unifies the directions, actions and intentions is the actual city of Memphis. Thus motion seems to consist in taking potency as such and adding various determinations to it that all hang on the reality of the act of the potency as actual.

When I speak of “adding determinations” this includes things that will be most simply described as sorts of removal. A taut bowstring, for example, is a potency as such to the flight of the arrow, and in order to have motion we need to remove an impediment to the target, sc. the fingers we clutch around the string. But the impediment we remove is precisely an impediment to the target, and so is defined in relation to the act of the potency as actual.

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