But that I consider rather as a negation of relation, than as anything real or positive.

Difference is of two kinds as opposed either to identity or resemblance.

The first is called a difference of number; the other of KIND.
SECT.VI.OF MODES AND SUBSTANCES I would fain ask those philosophers, who found so much of their reasonings on the distinction of substance and accident, and imagine we have clear ideas of each, whether the idea of substance be derived from the impressions of sensation or of reflection?
If it be conveyed to us by our senses, I ask, which of them; and after what manner?
If it be perceived by the eyes, it must be a colour; if by the ears, a sound; if by the palate, a taste; and so of the other senses.

But I believe none will assert, that substance is either a colour, or sound, or a taste.
The idea, of substance must therefore be derived from an impression of reflection, if it really exist.

But the impressions of reflection resolve themselves into our passions and emotions: none of which can possibly represent a substance.