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we employ it about, but even comes short of that too: but how far it
reaches, let us now inquire.

7. How far our Knowledge reaches.

The affirmations or negations we make concerning the ideas we have, may,
as I have before intimated in general, be reduced to these four sorts,
viz. identity, co-existence, relation, and real existence. I shall
examine how far our knowledge extends in each of these:

8. 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. Because the Connexion between simple Ideas in substances is for the
most part unknown.

This, how weighty and considerable a part soever of human science, is
yet very narrow, and scarce any at all. The reason whereof is, that the
simple ideas whereof our complex ideas of substances are made up are,
for the most part, such as carry with them, in their own nature, no
VISIBLE NECESSARY connexion or inconsistency with any other simple
ideas, whose co-existence with them we would inform ourselves about.

11. Especially of the secondary Qualities of Bodi