The novel frequently explores questions about the nature and strength of self-identity. Characters like Anse, Cash, Jewel, and the Tulls demonstrate a clear sense of self. However, Faulkner uses Darl and Vardaman to examine the delicate nature of identity. Vardaman often defines his relationships with others by repeatedly stating, "Darl is my brother" and the more famous line, "My mother is a fish." Through these repeated phrases, Faulkner shows Vardaman's developing sense of identity as he connects with those around him.

For Vardaman, this identity formation is a continual and evolving process. In contrast, for Darl, it remains forever unfinished. The lack of his mother's affection alienates Darl not just from others but also from himself. He underscores the difference between himself and Jewel by saying, "I don't know what I am. I don't know if I am or not. Jewel knows he is because he does not know that he does not know whether he is or not." These lines make Darl's reflections both intriguing and disturbing, questioning the very core of human consciousness.