19. We have ordinarily as clear a notion of the relation, as of the simple ideas in things on which it is founded.
Secondly, That in relations, we have for the most part, if not always, as clear a notion of the relation as we have of
those simple ideas wherein it is founded: agreement or disagreement, whereon relation depends, being things
whereof we have commonly as clear ideas as of any other whatsoever; it being but the distinguishing simple
ideas, or their degrees one from another, without which we could have no distinct knowledge at all. For, if I have
a clear idea of sweetness, light, or extension, I have, too, of equal, or more, or less, of each of these: if I know
what it is for one man to be born of a woman, viz., Sempronia, I know what it is for another man to be born of the
same woman Sempronia; and so have as clear a notion of brothers as of births, and perhaps clearer. For if I
believed that Sempronia digged Titus out of the parsley-bed, (as they used to tell children), and thereby became
his mother; and that afterwards, in the same manner, she digged Caius out of the parsley-bed, I had as clear a
notion of the relation of brothers between them, as if I had all the skill of a midwife: the notion that the same
woman contributed, as mother, equally to their births, (though I were ignorant or mistaken in the manner of it),
being that on which I grounded the relation; and that they agreed in that circumstance of birth, let it be what it
will. The comparing them then in their descent from the same person, without knowing the particular
circumstances of that descent, is enough to found my notion of their having, or not having the relation of brothers.
But though the ideas of particular relations are capable of being as clear and distinct in the minds of those who
will duly consider them as those of mixed modes, and more determinate than those of substances: yet the names
belonging to relation are often of as doubtful and uncertain signification as those of substances or mixed modes;
and much more than those of simple ideas. Because relative words, being the marks of this comparison, which is
made only by men's thoughts, and is an idea only in men's minds, men frequently apply them to different
comparisons of things, according to their own imaginations; which do not always correspond with those of others
using the same name.
