The chapter opens with a voice cutting in: "Science has succeeded in so far analysing man that we know already that choice and what is called freedom of will is nothing else than, " The Underground Man stops them. He was about to say the same thing himself, he admits, but pulled back. Now he lets the argument be stated fully.
The rationalist case: if a mathematical formula is ever discovered for all human desires and caprices, which is surely possible, man will at once cease to feel desire. Who would want to choose by rule? He'd be transformed from a human being into an organ-stop. Everything could be calculated and tabulated: we'd choose according to tables, calculate our lives thirty years in advance. Nature does not ask our leave.
Here he stops and pushes back. Reason is an excellent thing, but it satisfies only the rational side of man's nature. Will, by contrast, is a manifestation of the whole life, the whole of it, including reason and all the impulses. There is one case, and one only, in which a man may consciously desire what is injurious to himself: simply to preserve his right to desire even what is stupid, and not to be bound to desire only what is sensible. And this caprice, this apparent madness, may be more advantageous than any advantage, because in any circumstances it preserves what is most precious: our personality, our individuality.
Then the history argument. What can be said about the history of mankind? That it is grand, yes, perhaps. Many-coloured, may be. Monotonous, possibly; it is mostly fighting. But the one thing that cannot be said about it is that it is rational. The very word sticks in one's throat. The most moral and rational men, sages and lovers of humanity, have sooner or later played some queer, unseemly trick. Shower a man with every earthly blessing, drown him in happiness and prosperity, leave him nothing to do but sleep and eat cakes, and out of sheer ingratitude he will still play you a nasty trick. He will desire the most fatal rubbish, the most uneconomical absurdity, simply to introduce into all this positive good sense his "fatal fantastic element." Simply to prove he is a man and not a piano-key.
And even if science proved mathematically that he IS a piano-key, he would purposely do something perverse out of ingratitude. He'd contrive destruction and chaos. He'd launch a curse upon the world, cursing being his privilege, the primary distinction between man and other animals. And if even chaos could be calculated and tabulated? Then man would purposely go mad to be rid of reason and gain his point. "The whole work of man really seems to consist in nothing but proving to himself every minute that he is a man and not a piano-key! It may be at the cost of his skin, it may be by cannibalism!"
The imagined rationalist fires back: no one is touching your free will, they simply want it to coincide with your own normal interests. His answer: "Good heavens, what sort of free will is left when it will all be a case of twice two makes four? Twice two makes four without my will. As if free will meant that!"
