Quincas Borba is the schoolmate of Brás Cubas who reappears, over the course of his life, in three guises: the beggar, the heir, and the philosopher of Humanitism. He dies mad, in Brás's house.
At school, he played emperor at the festivals. As an adult, Brás finds him at the Passeio Público, in worn clothes, dragging "the rags, as formerly the purple". He receives five milreis, kisses the banknote, refuses to work and announces the philosophy of misery; then he embraces Brás and steals his watch. Later he returns a new watch, with a letter announcing Humanitism, and appears in a frock coat and patent leather boots, heir to an uncle from Barbacena.
As a philosopher, he expounds the doctrine to Brás between the chicken and the coffee and begins to push him toward ambition: he encourages the marriage, urges him to found an opposition newspaper, and calls Brás's desire to be minister a whim. When Brás is downcast, he says that the worst philosophy is that of the crybaby who lies down on the riverbank.
The end is that of someone who knows what is happening to him: Quincas returns from Minas demented and aware of it, and dies in Brás's house, repeating that pain is an illusion. The same character reappears in Machado's next novel, Quincas Borba, which bears his name.