The theory of Quincas Borba is called Humanitas: the philosopher says that there is a single substance in all things, and Humanitism is the name of the doctrine he says he formulated. He defines it for Rubião as "a single, universal, eternal, common, indivisible and indestructible principle," and adds: "I call it that because it sums up the universe, and the universe is man."
He explains it through the death of his grandmother, knocked down by a carriage whose owner was hungry: "Humanitas needs to eat." From the death he draws the conclusion that there is no death, because the suppression of one form is the condition for the survival of another. Individuals are like bubbles that form and burst in boiling water, and to the question of the bubble's opinion he replies: "A bubble has no opinion." Before the bubbles, right after saying there is no death, comes the allegory of the two starving tribes, which ends with "To the victor, the potatoes" and shows that war conserves.
The philosopher applies it to several cases. The dog can have a human name because Humanitas exists in it too; illness and health are "two states of Humanitas"; in the letter in which he calls himself Saint Augustine, he writes: "I consider heresy everything that is not my doctrine of Humanitas." Rubião accepts being a disciple, but understands little.
What the book shows afterward is the use Rubião makes of it: he understands it only on inheriting, and in his mania he repeats the philosopher's theories, "at times using the same phrases," which he had not understood when he heard them in Barbacena. The narrator asks: "And why did all those reminiscences vanish with the return of reason?"