When we say, as Webster says, The definition of horse is A hoofed quadruped of the genus Equus, we may, in fact, mean three different things. (1) We may mean merely When I say horse, you are to understand that I am talking about a hoofed quadruped of the genus Equus. This might be called the arbitrary verbal definition: and I do not mean that good is indefinable in that sense. (2) We may mean, as Webster ought to mean: When most English people say horse, they mean a hoofed quadruped of the genus Equus. This may be called the verbal definition proper, and I do not say that good is indefinable in this sense either; for it is certainly possible to discover how people use a word: otherwise, we could never have known that good may be translated by gut in German and by bon in French. But (3) we may, when we define horse, mean something much more important. We may mean that a certain object, which we all of us know, is composed in a certain manner: that it has four legs, a head, a heart, a liver, etc., etc., all of them arranged in definite relations to one another. It is in this sense that I deny good to be definable. I say that it is not composed of any parts, which we can substitute for it in our minds when we are thinking of it. We might think just as clearly and correctly about a horse, if we thought of all its parts and their arrangement instead of thinking of the whole: we could, I say, think how a horse differed from a donkey just as well, just as truly, in this way, as now we do, only not so easily; but there is nothing whatsoever which we could substitute for good; and that is what I mean, when I say that good is indefinable. (§ 8 ¶ 1)