A man, if he compares two things together, can hardly be supposed not to know what it is wherein he compares them: so that when he compares any things together, he cannot but have a very clear idea of that relation.

THE IDEAS, THEN, OF RELATIONS, ARE CAPABLE AT LEAST OF BEING MORE PERFECT AND DISTINCT IN OUR MINDS THAN THOSE OF SUBSTANCES.

Because it is commonly hard to know all the simple ideas which are really in any substance, but for the most part easy enough to know the simple ideas that make up any relation I think on, or have a name for: v.g.comparing two men in reference to one common parent, it is very easy to frame the ideas of brothers, without having yet the perfect idea of a man.

For significant relative words, as well as others, standing only for ideas; and those being all either simple, or made up of simple ones, it suffices for the knowing the precise idea the relative term stands for, to have a clear conception of that which is the foundation of the relation; which may be done without having a perfect and clear idea of the thing it is attributed to.

Thus, having the notion that one laid the egg out of which the other was hatched, I have a clear idea of the relation of DAM and CHICK between the two cassiowaries in St.James's Park; though perhaps I have but a very obscure and imperfect idea of those birds themselves.
9.