When a man stubs his toe, for example, the facts that the injured member swells and that it hurts most frightfully appear to him as absolute certainties. If we deny that he actually knows these things and maintain that the spectacle of the swelling and the sensation of pain are mere creatures of his mind, we cast adrift from all order and common-sense in the universe and go sailing upon a stormy sea of crazy metaphysics and senseless contradictions. There are many things that we do not know, and in the nature of things, never can know. We do not know _why_ phosphorus has a tendency to combine with oxygen, but the fact that it _has_ we _do_ know--and if we try to deny we _do_ know it, we must deny that we are sentient beings, and in consequence, must regard life and the universe as mere illusions. No man with a sound mind makes any such denial. The things about us are real, just as our feeling that we are alive is real.[4] From this it must be plain that the superman will have the same guides that we have, viz.: his instincts and senses. But in him they will be more accurate and more acute than in us, because the whole tendency of his scheme of things will be to fortify and develop them.[5] If any race of Europe devoted a century to exercising its right arms, its descendants, in the century following, would have right arms like piston-rods. In the same way, the superman, by subordinating everything else to his instinct to live, will make it evolve into something very accurate and efficient. His whole concern, in brief, will be to live as long as possible and so to avoid as much as possible all of those things which shorten life--by injuring the body from without or by using up energy within. As a result he will cease all effort to learn _why_ the world exists and will devote himself to acquiring knowledge _how_ it exists. This knowledge _how_ will be within his capacity even more than it is within our capacity today. Our senses, as we have seen, have given us absolute knowledge that stubbing the toe results in swelling and pain. The superman's developed senses will give him absolute knowledge about everything that exists on earth. He will know exactly _how_ a tubercle bacillus attacks the lung tissue, he will know exactly _how_ the blood fights the bacillus, and he will know exactly _how_ to interfere in this battle in such a manner that the blood shall be invariably victorious. In a word, he will be the possessor of exact and complete knowledge regarding the working of all the benign and malignant forces in the world about him, but he will not bother himself about insoluble problems. He will waste no time speculating as to _why_ tubercle bacilli were sent into the world: his instinct to live will be satisfied by his success in stamping them out.