I may be answered that, according to the rules of motion among bodies, one ought to shake or move another. But where are those laws of motion written and recorded? Who both made them and rendered them so inviolable? They do not belong to the essence of bodies, for we can conceive bodies at rest; and we even conceive bodies that would not communicate their motion to others unless these rules, with whose original we are unacquainted, subjected them to it. Whence comes this, as it were, arbitrary government of motion over all bodies? Whence proceed laws so ingenious, so just, so well adapted one to the other, that the least alteration of or deviation from which would, on a sudden, overturn and destroy all the excellent order we admire in the universe? A body being entirely distinct from another, is in its nature absolutely independent from it in all respects. Whence it follows that it should not receive anything from it, or be susceptible of any of its impressions. The modifications of a body imply no necessary reason to modify in the same manner another body, whose being is entirely independent from the being of the first. It is to no purpose to allege that the most solid and most heavy bodies carry or force away those that are less big and less solid; and that, according to this rule, a great leaden ball ought to move a great ball of ivory. We do not speak of the fact; we only inquire into the cause of it. The fact is certain, and therefore the cause ought likewise to be certain and precise. Let us look for it without any manner of prepossession or prejudice. What is the reason that a great body carries off a little one? The thing might as naturally happen quite otherwise; for it might as well happen that the most solid body should never move any other body—that is to say, motion might be incommunicable. Nothing but custom obliges us to suppose that Nature ought to act as it does.
SECT. LXXXI. To give a satisfactory Account of Motion we must recur to the First Mover.
Moreover, it has been proved that matter cannot be either infinite or eternal; and, therefore, there must be supposed both a first atom (by which motion must have begun at a precise moment), and a first concourse of atoms (that must have formed the first combination). Now, I ask what mover gave motion to that first atom, and first set the great machine of the universe a-going? It is not possible to elude this home question by an endless circle, for this question, lying within a finite circumference, must have an end at last; and so we must find the first atom in motion, and the first moment of that first motion, together with the first mover, whose hand made that first impression.
SECT. LXXXII. No Law of Motion has its Foundation in the Essence of the Body; and most of those Laws are Arbitrary.
Among the laws of motion we must look upon all those as arbitrary which we cannot account for by the very essence of bodies. We have already made out that no motion is essential to any body. Wherefore all those laws which are supposed to be eternal and immutable are, on the contrary, arbitrary, accidental, and made without cogent necessity; for there is none of them that can be accounted for by the essence of bodies.
If there were any law of motion essential to bodies, it would undoubtedly be that by which bodies of less bulk and less solid are moved by such as have more bulk and solidity. And yet we have seen that that very law is not to be accounted for by the essence of bodies. There is another which might also seem very natural—that, I mean, by which bodies ever move rather in a direct than a crooked line, unless their motion be otherwise determined by the meeting of other bodies. But even this rule has no foundation in the essence of matter. Motion is so very accidental, and super-added to the nature of bodies, that we do not find in this nature of bodies any primitive or immutable law by which they ought to move at all, much less to move according to certain rules. In the same manner as bodies might have existed, and yet have never either been in motion or communicated motion one to another, so they might never have moved but in a circular line, and this motion might have been as natural to them as the motion in a direct line. Now, who is it that pitched upon either of these two laws equally possible? What is not determined by the essence of bodies can have been determined by no other but Him who gave bodies the motion they had not in their own essence. Besides, this motion in a direct line might have been upwards or downwards, from right to left, or from left to right, or in a diagonal line. Now, who is it that determined which way the straight line should go?
SECT. LXXXIII. The Epicureans can draw no Consequence from all their Suppositions, although the same should be granted them.
Let us still attend the Epicureans even in their most fabulous suppositions, and carry on the fiction to the last degree of complaisance. Let us admit motion in the essence of bodies, and suppose, as they do, that motion in a direct line is also essential to all atoms. Let us bestow upon atoms both a will and an understanding, as poets did on rocks and rivers. And let us allow them likewise to choose which way they will begin their straight line. Now, what advantage will these philosophers draw from all I have granted them, contrary to all evidence? In the first place, all atoms must have been in motion from all eternity; secondly, they must all have had an equal motion; thirdly, they must all have moved in a direct line; fourthly, they must all have moved by an immutable and essential law.
I am still willing to gratify our adversaries, so far as to suppose that those atoms are of different figures, for I will allow them to take for granted what they should be obliged to prove, and for which they have not so much as the shadow of a proof. One can never grant too much to men who never can draw any consequence from what is granted them; for the more absurdities are allowed them, the sooner they are caught by their own principles.