John Locke

“ For father and son, husband and wife, and such other correlative terms, seem so nearly to belong one to another, and, through custom, do so readily chime and answer one another in people’s memories, that, upon the naming of either of them, the thoughts are presently carried beyond the thing so named ; and nobody overlooks or doubts of a relation, where it is so plainly intimated. But where languages have failed to give correlative names, there the relation is not always so easily taken notice of. ”

“ Thus, when the mind considers Caius as such a positive being, it takes nothing into that idea but what really exists in Caius ; v.g. when I consider him as a man, I have nothing in my mind but the complex idea of the species, man. So likewise, when I say Caius is a white man, I have nothing but the bare consideration of a man who hath that white colour. ”

“ Change of relation may be without any change in the things related. The nature therefore of relation consists in the referring or comparing two things one to another ; from which comparison one or both comes to be denominated. And if either of those things be removed, or cease to be, the relation ceases, and the denomination consequent to it, though the other receive in itself no alteration at all : v.g. Caius, whom I consider to-day as a father, ceases to be so to-morrow, only by the death of his son, without any alteration made in himself. ”

“ Terms leading the mind beyond the subject denominated, are relative. Fourthly, That relation being the considering of one thing with another which is extrinsical to it, it is evident that all words that necessarily lead the mind to any other ideas than are supposed really to exist in that thing to which the words are applied are relative words : v.g. a man, black, merry, thoughtful, thirsty, angry, extended ; these and the like are all absolute, because they neither signify nor intimate anything but what does or is supposed really to exist in the man thus denominated ”

“ 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. ”

“ These and the like relations, expressed by relative terms that have others answering them, with a reciprocal intimation, as father and son, bigger and less, cause and effect, are very obvious to every one, and everybody at first sight perceives the relation. ”

“ To clear this, I shall show it in the most considerable relations that we have any notion of ; and in some that seem to be the most remote from sense or reflection : which yet will appear to have their ideas from thence, and leave it past doubt that the notions we have of them are but certain simple ideas, and so originally derived from sense or reflection. ”