and the utmost unmoved walls or shell thereof to be the place whereby
they estimate true motions. If we sound our own conceptions, I believe we
may find all the absolute motion we can frame an idea of to be at bottom
no other than relative motion thus defined. For, as has been already
observed, absolute motion, exclusive of all external relation, is
incomprehensible; and to this kind of relative motion all the
above-mentioned properties, causes, and effects ascribed to absolute
motion will, if I mistake not, be found to agree. As to what is said of
the centrifugal force, that it does not at all belong to circular
relative motion, I do not see how this follows from the experiment which
is brought to prove it. See Philosophiae Naturalis Principia Mathematica,
in Schol. Def. VIII. For the water in the vessel at that time wherein it
is said to have the greatest relative circular motion, has, I think, no
motion at all; as is plain from the foregoing section.

115. For, to denominate a body moved it is requisite, first, that it
change its distance or situation with regard to some other body; and
secondly, that the force occasioning that change be applied to it. If
either of these be wanting, I do not think that, agreeably to the sense
of mankind, or the propriety of language, a body can be said to be in
motion. I grant indeed that it is possible for us to think a body which
we see change its distance from some other to be moved, though it have no
force applied to it (in which sense there may be apparent motion), but
then it is because the force causing the change of distance is imagined
by us to be applied or impressed on that body thought to move; which
indeed shows we are capable of mistaking a thing to be in motion which is
not, and that is all.

116. ANY IDEA OF PURE SPACE RELATIVE.--From what has been said it follows
that the philosophic consideration of motion does not imply the
being of an absolute Space, distinct from that which is perceived
by sense and related bodies; which that it cannot exist without the
mind is clear upon the same principles that demonstrate the like
of all other objects of sense. And perhaps, if we inquire narrowly,
we shall find we cannot even frame an idea of pure Space exclusive
of all body. This I must confess seems impossible, as being a mos
abstract idea. When I excite a motion in some part of my body,
if it be free or without resistance, I say there is Space; but if I
find a resistance,