s the identity of the whole, let we must measure the
greatness of the part, not absolutely, but by its proportion to the
whole. The addition or diminution of a mountain would not be sufficient
to produce a diversity in a planet: though the change of a very few
inches would be able to destroy the identity of some bodies. It will be
impossible to account for this, but by reflecting that objects operate
upon the mind, and break or interrupt the continuity of its actions not
according to their real greatness, but according to their proportion to
each other: And therefore, since this interruption makes an object cease
to appear the same, it must be the uninterrupted progress o the thought,
which constitutes the imperfect identity.

This may be confirmed by another phenomenon. A change in any
considerable part of a body destroys its identity; but it is remarkable,
that where the change is produced gradually and insensibly we are less
apt to ascribe to it the same effect. The reason can plainly be no
other, than that the mind, in following the successive changes of the
body, feels an easy passage from the surveying its condition in one
moment to the viewing of it in another, and at no particular time
perceives any interruption in its actions. From which continued
perception, it ascribes a continued existence and identity to the
object.

But whatever precaution we may use in introducing the changes gradually,
and making them proportionable to the whole, it is certain, that where
the changes are at last observed to become considerable, we make a
scruple of ascribing identity to such different objects. There is,
however, another artifice, by which we may induce the imagination to
advance a step farther; and that is, by producing a reference of the
parts to each other, and a combination to some common end or purpose.
A ship, of which a considerable part has been changed by frequent
reparations, is still considered as the same; nor does the difference
of the materials hinder us from ascribing an identity to it. The
common end, in which the parts conspire, is the same under all their
variations, and affords an easy transition of the imagination from one
situation of the body to another.

But this is still more remarkable, when we add a sympathy of parts
to their common end, and suppose that they bear to each other, the
reciprocal relation of cause and effect in all their actions and
operations. This is the case with all animals a