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 ideas of these different and interrupted perceptions, is almost the same disposition of mind with that in which we consider one constant and uninterrupted perception.  It is therefore very natural for us to mistake the one for the other.

[Footnote 9 This reasoning, it must be confest, is somewhat abstruse, and difficult to be comprehended; but it is remarkable, that this very difficulty may be converted into a proof of the reasoning.  We may observe, that there are two relations, and both of them resemblances, which contribute to our mistaking the succession of our interrupted perceptions for an identical object.  The first is, the resemblance of the perceptions:  The second is the resemblance, which the act of the mind in surveying a succession of resembling objects bears to that in surveying an identical object.  Now these resemblances we are apt to confound with each other; and it is natural we shoud, according to this very reasoning.  But let us keep them distinct, and we shall find no difficulty in conceiving the precedent argument.]

The persons, who entertain this opinion concerning the identity of our resembling perceptions, are in general an the unthinking and unphilosophical part of mankind, (that is, all of us, at one time or other) and consequently such as suppose their perceptions to be their only objects, and never think of a double existence internal and external, representing and represented.  The very image, which is present to the senses, is with us the real body; and it is to these interrupted images we ascribe a perfect identity.