the same body may move sometimes quicker and sometimes
slower; if a body that moves communicates its motion to the
neighbouring body that was at rest, or in such inferior motion that
it was insensible--it must be confessed that a mode or modification
which sometimes increases, and at other times decreases, in bodies
is not essential to them. What is essential to a being is ever the
same in it. Neither the motion that varies in bodies, and which,
after having increased, slackens and decreases to such a degree as
to appear absolutely extinct and annihilated; nor the motion that is
lost, that is communicated, that passes from one body to another as
a foreign thing--can belong to the essence of bodies. And,
therefore, I may conclude that bodies are perfect in their essence
without ascribing to them any motion. If they have no motion in
their essence, they have it only by accident; and if they have it
only by accident, we must trace up that accident to its true cause.
Bodies must either bestow motion on themselves, or receive it from
some other being. It is evident they do not bestow it on
themselves, for no being can give what it has not in itself. And we
are sensible that a body at rest ever remains motionless, unless
some neighbouring body happens to shake it. It is certain,
therefore, that no body moves by itself, and is only moved by some
other body that communicates its motion to it. But how comes it to
pass that a body can move another? What is the reason that a ball
which a man causes to roll on a smooth table (billiards, for the
purpose) cannot touch another without moving it? Why was it not
possible that motion should not ever communicate itself from one
body to another? In such a case a ball in motion would stop near
another at their meeting, and yet never shake it.

SECT. LXXX. The Rules of Motion, which the Epicureans suppose do
not render it essential to Bodies.

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 bodie