When we have been accustomed to observe a constancy in certain impressions, and have found, that the perception of the sun or ocean, for instance, returns upon us after an absence or annihilation with like parts and in a like order, as at its first appearance, we are not apt to regard these interrupted perceptions as different, (which they really are) but on the contrary consider them as individually the same, upon account of their resemblance. But as this interruption of their existence is contrary to their perfect identity, and makes us regard the first impression as annihilated, and the second as newly created, we find ourselves somewhat at a loss, and are involved in a kind of contradiction. In order to free ourselves from this difficulty, we disguise, as much as possible, the interruption, or rather remove it entirely, by supposing that these interrupted perceptions are connected by a real existence, of which we are insensible. This supposition, or idea of continued existence, acquires a force and vivacity from the memory of these broken impressions, and from that propensity, which they give us, to suppose them the same; and according to the precedent reasoning, the very essence of belief consists in the force and vivacity of the conception. In order to justify this system, there are four things requisite. First, To explain the PRINCIPIUM INDIVIDUATIONIS, or principle of identity. Secondly, Give a reason, why the resemblance of our broken and interrupted perceptions induces us to attribute an identity to them. Thirdly, Account for that propensity, which this illusion gives, to unite these broken appearances by a continued existence. Fourthly and lastly, Explain that force and vivacity of conception, which arises from the propensity. First, As to the principle of individuation; we may observe, that the view of any one object is not sufficient to convey the idea of identity. For in that proposition, an object is the same with itself, if the idea expressed by the word, object, were no ways distinguished from that meant by itself; we really should mean nothing, nor would the proposition contain a predicate and a subject, which however are implyed in this affirmation. One single object conveys the idea of unity, not that of identity. On the other hand, a multiplicity of objects can never convey this idea, however resembling they may be supposed. The mind always pronounces the one not to be the other, and considers them as forming two, three, or any determinate number of objects, whose existences are entirely distinct and independent.