The style of Notes from Underground changes drastically from Part 1 to Part 2. Part 1 has no narrative or characters beyond The Underground Man, but it details his philosophical musings and arguments. The only dialogue featured in it is between himself and the imaginary reader, where he justifies his positions:
Well, now, for example, someone might seize upon my words and ask me, if you really aren’t counting on any readers, why do you make such compacts with yourself, and on paper no less; that is, if you’re not going to introduce any order or system, if you’re going to write down whatever comes to mind, etc., etc.? Why do you go on explaining? Why do you keep apologizing?
“Well, imagine that,” I reply.
This excerpt also exemplifies the prose style of Part 1. The Underground Man writes with long, winding sentences, which is characteristic of 19th-century Russian writing. The Underground Man's insistence on using it not to describe his world, as was often the case for other writers (and for Dostoevsky, in his later novels), but to argue his point signals The Underground Man's mental instability and distance from society in using this style. The Underground Man often writes with compound-complex sentences throughout Part 1, a style that changes drastically during Part 2.
Part 2 is more narrative, showing how the narrator became The Underground Man. It details his discomfort with society and being driven into the underground. The sentences are shorter, and the prose is filled with dialogue, following a narrative instead of The Underground Man's philosophical argument. His philosophy as it was when he was in his 20s (which would later develop into the arguments the reader finds in Part 1) are only shown through dialogue. He finds himself an outcast and tries to justify it by showing how other people treated him, but he still sees himself as someone who cannot fit into society.
Throughout the whole of the novella, the prose is full of allusions to popular ideas and philosophies of the time. For example, The Underground Man refers to Heinrich Heine, who argued that Jean-Jacques Rousseau's autobiographical Confessions were untrue and believed that people were sure to lie about themselves. The Underground Man responds to this claim by wondering whether it is possible to be entirely true, even with oneself. As the philosophical musings in Notes from Underground directly respond to arguments and ideas popular at the time, such as a pessimistic view of human nature and the belief that people are inherently irrational, it makes sense for Dostoevsky to directly allude to the ideas he criticizes.