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?