A water-baby? You never heard of a water-baby. Perhaps not. That is the very reason why this story was written. There are a great many things in the world which you never heard of; and a great many more which nobody ever heard of; and a great many things, too, which nobody will ever hear of, at least until the coming of the Cocqcigrues, when man shall be the measure of all things. "But there are no such things as water-babies." How do you know that? Have you been there to see? And if you had been there to see, and had seen none, that would not prove that there were none. And no one has a right to say that no water-babies exist, till they have seen no water-babies existing; which is quite a different thing, mind, from not seeing water-babies; and a thing nobody ever did, or perhaps ever will do. "But surely if there were water-babies, somebody would have caught one at least?" Well. How do you know that somebody has not? "But they would have put it into spirits, or into the _Illustrated News_, or perhaps cut it into two halves, poor dear little thing, and sent one to Professor Owen, and one to Professor Huxley, to see what they would each say about it." Ah, my dear little man! that does not follow at all, as you will see before the end of the story. "But a water-baby is contrary to nature." Well, but, my dear little man, you must learn to talk about such things, when you grow older, in a very different way from that. You must not talk about "ain't" and "can't" when you speak of this great wonderful world round you, of which the wisest man knows only the very smallest corner, and is, as the great Sir Isaac Newton said, only a child picking up pebbles on the shore of a boundless ocean. You must not say that this cannot be, or that that is contrary to nature. You do not know what Nature is, or what she can do; and nobody knows. Wise men are afraid to say that there is anything contrary to nature, except what is contrary to mathematical truth; for two and two cannot make five, and two straight lines cannot join twice, and a part cannot be as great as the whole, and so on (at least, so it seems at present): but the wiser men are, the less they talk about "cannot." That is a very rash, dangerous word, that "cannot"; and if people use it too often, the Queen of all the Fairies, who makes the clouds thunder and the fleas bite, and takes just as much trouble about one as about the other, is apt to astonish them suddenly by showing them, that though they say she cannot, yet she can, and what is more, will, whether they approve or not.