The central theme is a life without achievement, told by someone who, being dead, says what the living keep silent about: the interest that drives people of his class, starting with the narrator himself.
Three threads run through the book. The first is the fixed idea of glory: the plaster is born from the taste of seeing one's name in print, the father wants his son a deputy, and Brás wants to be minister and never gets there. The second is love and its price: Marcela loves him "for fifteen months and eleven contos de réis", and the affair with Virgília, who is married, requires a hidden little house and a guardian, because she does not separate love from public esteem. The third is the law of the victor: in the delirium, Nature explains that the jaguar kills the young bull because the jaguar's reasoning is that it must live; the boy Brás rides the servant Prudêncio, and Prudêncio, already freed, beats in the street an enslaved man who belongs to him. Quincas Borba gives this law a doctrine, Humanitism.
There is also the theme of the form itself. The narrator interrupts the story, talks with the reader, corrects earlier chapters and writes chapters of one line, so that the way of telling becomes a subject of the book. Brás defines the work as "uneven philosophy" and, in the prologue, says he wrote it "with the pen of jest and the ink of melancholy": laughter is the instrument, and melancholy the matter.