But enough has perhaps been said. As the fish in the sea, or the bird in the air, so unreasoningly and inarticulately safe must a man feel before he can be said to know. It is only those who are ignorant and uncultivated who can know anything at all in a proper sense of the words. Cultivation will breed in any man a certainty of the uncertainty even of his most assured convictions. It is perhaps fortunate for our comfort that we can none of us be cultivated upon very many subjects, so that considerable scope for assurance will still remain to us; but however this may be, we certainly observe it as a fact that the greatest men are they who are most uncertain in spite of certainty, and at the same time most certain in spite of uncertainty, and who are thus best able to feel that there is nothing in such complete harmony with itself as a flat contradiction in terms. For nature hates that any principle should breed, so to speak, hermaphroditically, but will give to each an help meet for it which shall cross it and be the undoing of it; as in the case of descent with modification, of which the essence would appear to be that every offspring should resemble its parents, and yet, at the same time, that no offspring should resemble its parents. But for the slightly irritating stimulant of this perpetual crossing, we should pass our lives unconsciously as though in slumber. Until we have got to understand that though black is not white, yet it may be whiter than white itself (and any painter will readily paint that which shall show obviously as black, yet it shall be whiter than that which shall show no less obviously as white), we may be good logicians, but we are still poor reasoners. Knowledge is in an inchoate state as long as it is capable of logical treatment; it must be transmuted into that sense or instinct which rises altogether above the sphere in which words can have being at all, otherwise it is not yet vital. For sense is to knowledge what conscience is to reasoning about right and wrong; the reasoning must be so rapid as to defy conscious reference to first principles, and even at times to be apparently subversive of them altogether, or the action will halt. It must, in fact, become automatic before we are safe with it. While we are fumbling for the grounds of our conviction, our conviction is prone to fall, as Peter for lack of faith sinking into the waves of Galilee; so that the very power to prove at all is an _à priori_ argument against the truth—or at any rate the practical importance to the vast majority of mankind—of all that is supported by demonstration. For the power to prove implies a sense of the need of proof, and things which the majority of mankind find practically important are in ninety-nine cases out of a hundred above proof. The need of proof becomes as obsolete in the case of assumed knowledge, as the practice of fortifying towns in the middle of an old and long settled country.