The Underground Man realizes that some people will object to his ideas by saying that choice and freedom of will can be reduced to a mathematical formula. But, he explains, if things are explained scientifically, then man will cease to feel desire, for if reason and desire should conflict, man would be compelled to follow reason and this would lead to a senseless, mechanistic existence. One could then calculate one's entire life for thirty years beforehand and have nothing more to do but follow a mechanical existence. The prospect of such a life is repulsive. Man is made up of both reason and impulses, and thus man's life is made more meaningful by wanting to respond with all his capacities and not with just his capacity for reasoning. This caprice and these non-rational desires are in reality a great ad-vantage to man because they are what define his personality and individuality.
The Underground Man argues further that the history of the world proves that man is not rational. The whole of man's life consists of "proving to himself every minute that he is a man" and not a predictable cog in a logical mechanism.
The Underground Man continues his attack against a utopian society in which man would become a mechanistic robot. In such a scientific society, even choice and freedom of will would be reduced to "two times two makes four." If everything is known beforehand, if everything can be predicted with mathematical certainty, the Underground Man points out that under such conditions, man will lose certain valuable aspects of his basic humanity. For example, if it is pointed out with mathematical and scientific certainty that when desires and emotions conflict with logic, then man must "cease to feel desire, and instead perform the logical act, and if man's acts can thus be predicted with logical certainty, life would then be dull and boring, and man would become a mechanistic peg in a large machine. He would become an "organ-stop" or a "piano key," and thus lose part of his humanity. "For what is a man without desires, without free will and without choice, if not a stop in an organ."
The point the Underground Man is leading to is that the nature of man is not defined by his intellectual achievements alone. Thus, a scientific society would be catering to and satisfying "only the rational side of man's nature." Instead, the entirety of man is made up of part reason and Part 1mpulse (or caprice). A scientific, rational society would then satisfy only one's capacity for reason and not one's capacity for life in its entirety. Such a society, rather than benefiting man, would deny an essential part of his nature; that is, his irrational impulse, desire, emotion, or caprice.
For the Underground Man, freedom of choice, the freedom to commit irrational acts, is the very quality which defines man's personality and his individuality. Without this quality, man be-comes a mechanical robot performing routine acts. Consequently, man often deliberately performs irrational acts, deliberately encounters chaos and destruction for no other purpose than to assert his individuality and prove that he is free.