One approach to The Sound and the Fury is by evaluating each brother's relationship to Caddy. We have no direct view of her — only the reports of Benjy, Quentin, and Jason. From these reports, we have to judge what type of person she actually was.
In our earliest view of Caddy, we see her at the branch as a rather daring young girl. She is not concerned with appearance; instead, she searches for the truth and reality of any situation. It is Caddy who climbs the tree to see exactly what is happening at her grandmother's funeral.
Caddy must also function as a type of mother. Even in the early scenes, Mr. Compson asks Caddy to look after Benjy because Mrs. Compson is sick. As a consequence, Benjy develops a strong love and need for Caddy. She replaces the love that is denied him by his own mother. Whenever Mrs. Compson tries to correct Benjy, it is only Caddy who can quiet Benjy. She even sends her mother upstairs "so you can be sick." Caddy, at a very early age, has to perform the functions of a mother.
As Caddy grows older, she sees through the neurotic whining of mother and the weakness and cynicism of her father. She feels the need to reject this artificial world and look for some way to reject everything concerned with the Compson world. She later admits that she does not love the men with whom she has sex, and she also says that she made them have sex with her. Why? Caddy's actions are deliberate forms of rejection. She has seen through the false concept of honor and the superficiality of the entire so-called aristocratic world. She becomes the complete realist, someone who simply cannot tolerate the hypocrisy and artificiality and false pride of the Compsons; therefore, she turns to unorthodox behavior in an attempt to assert her own independence and individuality.
Caddy does not enjoy her relationships with men and tells Quentin that "when they touched me, I died." Her relationships are deliberate forms of rejection of the Compson world. When Quentin offers suicide or incest to her, Caddy is willing to do either of these because either act would be a strong act of rejection. She believes that there is a curse on the entire Compson family, and, therefore, she is willing to attempt any violation of order (even incest or suicide) in order to escape from the horror of the Compson world. Her acts are performed in an attempt to assert her own individuality against a mother and father who have essentially rejected her or have, in some way, failed her.