Definition of Tone
The Underground Man's tone is pompous and self-serving, as he often positions himself as better and more rational than others. This disconnection from others in society leads him into isolation, and his time underground only makes his self-righteousness stronger. It is clear in his ramblings that he sees himself as greater and smarter than his contemporaries, and even when he makes a rational and reasonable argument, he makes sure to compliment himself during it. He writes long, rambling sentences that he expects the reader to follow without often clarifying himself, as he writes for his own satisfaction.
The confident and assured tone stays consistent throughout the Notes, but the narrator also simultaneously disparages himself as he recalls the way he acted in society before going underground. He sees himself as awkward and feels like an outcast in his workplace, despite his best efforts, and his tone changes to judge himself for his various mistakes while scorning those who wronged him. The people who wronged him seem to be everyone, as he describes his time in society as making him a pariah intellectually and socially.
Despite the philosophical nature of the Notes, the tone is mostly focused inward. When The Underground Man critiques a particular philosophy or idea, he does it with relation to himself, not the world at large. He thinks about rationality regarding how he himself thinks. Since he has been underground for 20 years and has not socialized in that time, this makes sense, but it does lend itself to a self-serving and narcissistic tone throughout the novella.