different perception or idea, which may require a different direction of
the spirits, in order to its conception.

Now what other objects, beside identical ones, are capable of placing
the mind in the same disposition, when it considers them, and of causing
the same uninterrupted passage of the imagination from one idea to
another? This question is of the last importance. For if we can find any
such objects, we may certainly conclude, from the foregoing principle,
that they are very naturally confounded with identical ones, and are
taken for them in most of our reasonings. But though this question be
very important, it is not very difficult nor doubtful. For I immediately
reply, that a succession of related objects places the mind in this
disposition, and is considered with the same smooth and uninterrupted
progress of the imagination, as attends the view of the same invariable
object. The very nature and essence of relation is to connect our ideas
with each other, and upon the appearance of one, to facilitate the
transition to its correlative. The passage betwixt related ideas is,
therefore, so smooth and easy, that it produces little alteration on
the mind, and seems like the continuation of the same action; and as the
continuation of the same action is an effect of the continued view of
the same object, it is for this reason we attribute sameness to every
succession of related objects. The thought slides along the succession
with equal facility, as if it considered only one object; and therefore
confounds the succession with the identity.

We shall afterwards see many instances of this tendency of relation to
make us ascribe an identity to different objects; but shall here confine
ourselves to the present subject. We find by experience, that there is
such a constancy in almost all the impressions of the senses, that their
interruption produces no alteration on them, and hinders them not from
returning the same in appearance and in situation as at their first
existence. I survey the furniture of my chamber; I shut my eyes, and
afterwards open them; and find the new perceptions to resemble perfectly
those, which formerly struck my senses. This resemblance is observed in
a thousand instances, and naturally connects together our ideas of these
interrupted perceptions by the strongest relation, and conveys the
mind with an easy transition from one to another. An easy transition
or passage of the imagination, along the ide