What is Force?

1. In order to discover the truth, the most important thing is to not be misled by misunderstood words.

Yet this does not seem particularly difficult, especially in the treatment of physical matters, where sense perception, experience, and geometrical reasoning are applicable.

Therefore, putting aside, as much as possible, all prejudice arising both from customary speech and from the authority of philosophers, the nature of things themselves must be carefully examined.

For no one’s authority should carry so much weight that their words or expressions are accepted without clear and certain meaning being found beneath them.

2. The contemplation of motion greatly perplexed the minds of the ancient philosophers.

The following modern words have obscure and abstract meanings:

• solicitation of gravity
• effort
• dead forces, etc.

3. Solicitation and effort or striving properly apply only to animate beings.

When attributed to other things, they must necessarily be understood in a metaphorical sense.

But a philosopher should avoid metaphors. Moreover, if all emotional states of the soul and all bodily movements are excluded, anyone who seriously considers the matter will realize that nothing clear or distinct is signified by those words.

4. While we are supporting heavy bodies, we feel within ourselves effort, fatigue, and discomfort.

We also observe that heavy objects fall with accelerated motion toward the center of the Earth.

But apart from this, our senses reveal nothing more.

By reason, however, it is inferred that there must be some cause or principle of these phenomena; and this is commonly called gravity.

But since the cause of the descent of heavy bodies is hidden and unknown, gravity, in this sense, cannot properly be called a sensible quality.

It is thus an occult quality.

Yet it is hardly, or not at all, conceivable what an occult quality is, or how any quality could act or do anything.

It would therefore be better, setting aside the notion of occult qualities, for people:

• to attend only to sensible effects
• in contemplation, to lay aside abstract terms and fix the mind on particulars and concrete things—that is, on the things themselves.

5. Force is similarly attributed to bodies: the term is used as if it signified a known quality, distinct both from motion, shape, and all other sensible things, as well as from any emotion of a living being.

But on closer inspection, this turns out to be nothing more than another occult quality. Animal effort and bodily motion are commonly viewed as symptoms or measures of this occult quality.

6. It is therefore clear that gravity or force is in vain posited as a principle of motion.

For can that principle be more clearly known merely by calling it an occult quality?

That which is itself hidden explains nothing. And leaving aside the unknown efficient cause, it would be more accurate to call it a substance than a quality. Moreover, terms such as force, gravity, and the like are often, and not inappropriately, used in the concrete—to refer, for instance, to a moving body, resistance, etc. But when philosophers use them to signify certain natures abstracted from all such concrete things—natures which are neither subject to the senses nor intelligible to the mind nor imaginable—they then become sources of error and confusion.

7. Many are led into error by the fact that general and abstract terms appear useful for reasoning, without fully understanding their import.

These terms were partly invented by common usage to shorten speech and partly devised by philosophers for teaching—not because they are suited to the nature of things, which are always singular and concrete, but because they are useful for transmitting knowledge, by enabling concepts—or at least propositions—to be expressed universally.