Summary: Physics (page 4)

Book IV

What is the place?

The primary form of movement is that which occurs in relation to place — locomotion.

There are six directions: up, down, left, right, front, back.

Here, Aristotle presents his famous theory of the natural place, according to which every body has a place where it naturally belongs:

If nothing stands in the way, each moves towards its own place, one above, the other below ¹.

What is place made of? A mass of body? That is impossible, for then two bodies would be in the same place. The paradox of place is that it cannot belong to corporeal things or incorporeal things, it has indeed a magnitude but no body ².

Aristotle distinguishes between common place (the space containing all bodies) and particular place (the space where a body is immediately situated).

He defines place as the primary container of that of which it is the place ³.

He resolves Zeno's aporia — which holds that place must itself be in a place, leading to an absurd infinite regress — by showing that place can exist within a body as health is in warm bodies as a state, and warmth in the body as a property ⁴.

Since motion occurs within a container that remains at rest — place — the first immobile limit of the container, that is what the place is ⁵.

Thus the place is somewhere, not as in a place, but as the limit is in the limited ⁶.

The void is a type of place where nothing exists — a pure and empty space.

For Aristotle, the void does not exist. Those who defend the void argue that without it, motion would be impossible. It is quite the opposite for Aristotle: Not a single thing can be in motion if the vacuum exists; indeed in the vacuum there is necessarily rest, for there is nothing towards which a motion will more or less willingly move, since, as a vacuum, it possesses no difference ⁷.

Moreover, motion in a vacuum would be without limit, for nothing would impede it.

The vacuum exists neither in actuality nor even in potentiality.

Aristotle now examines the notion of time.

He sets out the famous paradox of time: time does not exist, for it consists of the past, which no longer is; the future, which is not yet; and the present, which is fleeting and perpetually vanishes.

Time is not motion, for motion can be faster or slower, whereas time admits of no such variation. However, time does not exist without change: no time seems to have passed when our thought remains unchanged. Thus, we say that time has passed when we perceive a change.

Thus time is neither movement nor without movement ⁸. It is therefore necessarily something of movement ⁹. What exactly? Here is the answer:

When we perceive the anterior and posterior, then we say there is time, for this is what time is: the number of motion according to the anterior and posterior ¹⁰.

Thus, since time is the measure of movement ¹¹, time is number ¹².

Time cannot exist without the soul, for number cannot exist without a numbering mind.

¹ Book IV, 208b
² ibid., 209a
³ ibid.,
⁴ ibid., 210b
⁵ ibid., 212a
⁶ ibid., 212b
⁷ ibid., 214b
⁸ ibid., 219a
⁹ ibid.
¹⁰ ibid., 219b
¹¹ ibid., 221a
¹² ibid.