Men observing certain qualities always joined and existing together, therein copied nature; and of ideas so united made their complex ones of substances.

For, though men may make what complex ideas they please, and give what names to them they will; yet, if they will be understood WHEN THEY SPEAK OF THINGS REALLY EXISTING, they must in some degree conform their ideas to the things they would speak of; or else men's language will be like that of Babel; and every man's words, being intelligible only to himself, would no longer serve to conversation and the ordinary affairs of life, if the ideas they stand for be not some way answering the common appearances and agreement of substances as they really exist.
29.

Our Nominal Essences of substances usually consist of a few obvious qualities observed in things.
Secondly, Though the mind of man, in making its complex ideas of substances, never puts any together that do not really, or are not supposed to, co-exist; and so it truly borrows that union from nature: yet the number it combines depends upon the various care, industry, or fancy of him that makes it.

Men generally content themselves with some few sensible obvious qualities; and often, if not always, leave out others as material and as firmly united as those that they take.

Of sensible substances there are two sorts: one of organized bodies, which are propagated by seed; and in these the SHAPE is that which to us is the leading quality, and most characteristical part, that determines the species.