Cannibalism operates as the central symbol in “Diary of a Madman.” Within the context of the story, cannibalism symbolizes societal domination, exploitation, and unjust social structures. Over the course of the story, the “madman” believes that not only do his neighbors harbor resentments toward him but also toward each other, leading them to conspire to eat their neighbors. Lu Xun expands the symbol of cannibalism to include other types of social injustice, including the power of parents over their children, government over the people, and the old over the young.

Through examining history, and in conversations with others, the “madman” realizes that cannibalism is an integral part of his society and that the practice goes back thousands of years. It is perpetuated through the generations as parents teach their children, who internalize and practice injustice. The “madman” seeks to change this system at several points in the story: first by demonstrating his own virtue, then by trying to convince others to change their ways, and finally by realizing that the only ones who can be saved are children.