Firstly, Our Knowledge of Identity and Diversity in ideas extends as far as our Ideas themselves.
FIRST, as to IDENTITY and DIVERSITY.

In this way of agreement or disagreement of our ideas, our intuitive knowledge is as far extended as our ideas themselves: and there can be no idea in the mind, which it does not, presently, by an intuitive knowledge, perceive to be what it is, and to be different from any other.
9.

Secondly, Of their Co-existence, extends only a very little way.
SECONDLY, as to the second sort, which is the agreement or disagreement of our ideas in CO-EXISTENCE, in this our knowledge is very short; though in this consists the greatest and most material part of our knowledge concerning substances.

For our ideas of the species of substances being, as I have showed, nothing but certain collections of simple ideas united in one subject, and so co-existing together; v.g.
our idea of flame is a body hot, luminous, and moving upward; of gold, a body heavy to a certain degree, yellow, malleable, and fusible: for these, or some such complex ideas as these, in men's minds, do these two names of the different substances, flame and gold, stand for.

When we would know anything further concerning these, or any other sort of substances, what do we inquire, but what OTHER qualities or powers these substances have or have not?
Which is nothing else but to know what OTHER simple ideas do, or do not co-exist with those that make up that complex idea?
10.