Physics

[Democritus] The OCR reads "tipus," likely a corruption of the name Democritus, who along with Leucippus founded the school of Atomism. and the followers of those who posited that the principles of things are indivisible bodies which are atoms—from a, meaning "without," and tomos, meaning "division"—said that it was not possible to see, nor to act, nor for any motion to exist except through a vacuum. Hence they said: if everything were a vacuum, it would be possible for a fly to be seen in the sky. Aristotle, however, says that not even an ox [could be seen]. He says that if everything were a vacuum, there would be no motion. For motion cannot happen through a vacuum, and he demonstrates this in the fourth book of the Physics thus:

The speed and slowness of motion are caused by the heaviness and lightness of the object that is moved, and by the thinness and thickness of the medium through which the motion occurs. Let it be assumed, therefore, that a very light body moves through a very thin medium; it is clear that this motion is the fastest, and the fastest motion is measured by the smallest time. For "fast" is, as Aristotle says, that which moves a lot in a little time; whereas "slow" is that which moves a little in [much] The OCR reads "nullo" (no time), but the logic of the argument and Aristotelian physics requires "multo" (much time). time. Therefore, if there were motion through a vacuum—since a vacuum infinitely exceeds even the thinnest medium (for a vacuum is a place lacking any body)—it follows that this motion would be faster than the "fastest," and consequently would be measured by a time smaller than the "smallest" time. But this is impossible. For no motion is faster than the fastest, and no time is less than the smallest; therefore, motion through a vacuum is not possible.

And this demonstration is useful for understanding how an angel moves from place to place, yet not through a medium. For an angel's motion is infinitely faster than any physical motion. Indeed, the motion of an angel is not measured by time, but by the now original: "nunc". In this context, it refers to a discrete instant rather than a continuous duration.. And if it is objected that between two "nows" there is a medium of time—and if the motion of an angel is measured by "now" and "now," it is therefore measured by time—it must be said that there is a flowing now flowing now (nunc fluens): the continuous "present" that creates the flow of time, and between two such "nows" there is a medium of time. But there is also a successive now successive now (nunc vicissitudinatum): discrete moments of change that do not form a continuous line, and between two such "nows" there is no medium of time; and by such a "now" is the motion of an angel measured. Aristotle therefore says that motion happens through what is actually full, and through a vacuum only in potentiality—as can be seen when someone moves through air or water.

On the definitions of motion. Chapter 8.

We must therefore see what motion is and how it is divided. Motion is thus defined by Aristotle in the third book of the Physics: motion is the entelechy original: "endelechia". A term used by Aristotle to describe the full realization or "actuality" of a potential. of that which exists, or of a being in potentiality, insofar as it is such; for example, the "alteration" of the alterable insofar as it is alterable. Also in the same book: motion is an "imperfect act." Likewise, Avicenna An influential Persian philosopher whose synthesis of Aristotelian thought was foundational for medieval scholars. defines motion thus: Motion is the exit from potentiality to actuality continuously and not suddenly. It is also defined this way: Motion is the "first perfection" of that which is in potentiality. So that these definitions may become clear, it should be known that some things are in potentiality such that their act is brought forth suddenly; and of these, there is no "motion." Others, however, are in potentiality...