And
just as we have remarked above that the same thing may be said to
change and not to change place at the same time, so also we may say
that the same thing is at the same time moved and not moved. Thus,
for example, a person seated in a vessel which is setting sail,
thinks he is in motion if he look to the shore that he has left, and
consider it as fixed; but not if he regard the ship itself, among
the parts of which he preserves always the same situation. Moreover,
because we are accustomed to suppose that there is no motion without
action, and that in rest there is the cessation of action, the
person thus seated is more properly said to be at rest than in
motion, seeing he is not conscious of being in action.
XXV. What motion is properly so called.
But if, instead of occupying ourselves with that which has no
foundation, unless in ordinary usage, we desire to know what ought
to be understood by motion according to the truth of the thing, we
may say, in order to give it a determinate nature, that it is THE
TRANSPORTING OF ONE PART OF MATTER OR OF ONE BODY FROM THE VICINITY
OF THOSE BODIES THAT ARE IN IMMEDIATE CONTACT WITH IT, OR WHICH WE
REGARD AS AT REST, to the vicinity of other bodies.
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