What is Force?

52. The Peripatetics, for the variety of changes which anything can undergo, distinguished various kinds of motion.

Today, those who discuss motion understand only local motion.

But local motion cannot be understood unless what place is is simultaneously understood: but this is defined by modern thinkers as the part of space which a body occupies: whence it is divided into relative and absolute according to the relation of space.

For they distinguish between absolute or true space, and relative or apparent space. They wish, namely, that there be a space everywhere immense, immobile, insensible, permeating and containing all bodies, which [pg 520] they call absolute space.

But the space comprehended or defined by bodies, and thus subject to the senses, is called relative, apparent, or vulgar space.

53. Let us imagine, therefore, all bodies to be destroyed and reduced to nothing.

What remains they call absolute space, all relation which arose from the situation and distances of bodies being removed, along with the bodies themselves. Furthermore, that space is infinite, immobile, indivisible, insensible, without relation and without distinction.

That is, all its attributes are privative or negative: it seems therefore to be a mere nothing.

It only raises some difficulty in that it is extended. But extension is a positive quality. But what kind of extension is that which can neither be divided nor measured, of which we can perceive no part by sense, nor depict it in imagination?

For nothing falls into imagination which, by the nature of the thing, it is not possible to perceive by sense; since imagination is nothing other than the representative faculty of sensible things, either actually existing, or at least possible.

Moreover, it escapes pure intellect, since that faculty is concerned only with spiritual and unextended things, such as our minds, and their habits, passions, virtues, and the like.

Therefore, let us remove the words from absolute space, and nothing will remain in sense, imagination, or intellect: therefore, nothing else is designated by them than pure privation or negation, that is, mere nothing.

55. We are sometimes deceived by the fact that, with all other bodies removed in imagination, we nevertheless suppose our own to remain.

We then imagine the motion of our limbs most freely from every side.

But motion cannot be conceived without space.

But if we are attentive, the following will be evident:

1. Relative space is conceived, defined by the parts of our body

2. The most free power of moving our limbs, unimpeded by any obstacle; and nothing besides these two.

3. We falsely believe that some third thing, namely immense space, really exists. We think that this gives us the free power of moving our body: for this only the absence of other bodies is required. Which absence, or privation of bodies, we must confess to be nothing positive.

Whatever is predicated of pure and absolute space, all of it can be predicated of nothing.

By which reasoning the human mind is most easily freed from great difficulties and at the same time from that absurdity of attributing necessary existence to anything other than the one best and greatest God.

This is proven by questions about absolute space.

For example, is it a substance or an accident? It is created or uncreated?

We then demonstrate the absurdities consequent on either side.

Democritus of old confirmed this opinion by his calculation, as Aristotle is the author in Physics I. i, where he has this: “Democritus posits the solid and the void as principles, of which he says the one indeed exists as what is, the other as what is not.”

If perhaps a scruple is raised that this distinction between absolute and relative space is used by philosophers of great name, and many excellent theorems are built upon it as a foundation, it will appear from what follows that this scruple is vain.

58. Therefore, it is not fitting for us to define::

• the true place of a body to be the part of absolute space which the body occupies
• the true or absolute motion to be the change of true and absolute place.

Every place is relative, as is every motion.

No motion can be understood without some determination or direction. This direction cannot be understood unless, besides the moved body, our own body, or some other, is understood to exist at the same time.

Up, down, left, right, and all directions and regions are founded on some relation.

These necessarily connote and presuppose a body distinct from the moved one.

If the remaining bodies were reduced to nothing, a single globe, for example, is supposed to exist.

• In it no motion can be conceived: so necessary is it that another body be given, by whose situation the motion is understood to be determined.

The truth of this opinion will shine forth most clearly, provided we have rightly supposed the annihilation of all bodies, both our own and others, except for that single globe.

59. Let two globes, and nothing else corporeal, be conceived to exist.

Let forces then be conceived to be applied in any way whatsoever: whatever we finally understand by the application of forces, the circular motion of the two globes around a common center cannot be conceived by the imagination.

Let the heaven of fixed stars then be created.

Suddenly, from the conceived approach of the globes to different parts of that heaven, motion will be conceived.

Namely, since motion by its nature is relative, it could not be conceived before correlated bodies were given. Just as no other relation can be conceived without correlates.