Hume refutes the existence of all material and immaterial substances. Hume thinks that the source of this error lies in the resemblance amongst what one might want to call "different time slices of the mental realm".
Hyde's memory, and converso modo, the latter cannot recall anything that the former does; in short, they do not have the same N. There is a very remarkable circumstance, that attends this experiment; which is, that tho' the change of any considerable part in a mass of matter destroys the identity of the whole, let we must measure the greatness of the part, not absolutely, but by its proportion to the whole.
If all our perceptions are different and independent to each other and there is no idea of self then, Hume questions how were they organized and related to each other.
For Hume perfect identity holds between a perception and an object if that perception is unchanging and uninterrupted. Block, O. And in this view our identity with regard to the passions serves to corroborate that with regard to the imagination, by the making our distant perceptions influence each other, and by giving us a present concern for our past or future pains or pleasures.
In order to justify to ourselves this absurdity, we often feign some new and unintelligible principle, that connects the objects together, and prevents their interruption or variation.
Book, 1 Part 4, Sect 2, P. And why do we attribute to it mistakenly the notion of sameness? This is only by the reason of imagiantion that we do with another objects.
He also believes that we often attribute identity in an improper sense, like when we attach the label to variable or interrupted objects. Hume did not consider personality as a necessarily stable characteristic of the individual.