Mama and Beneatha operate as foils in the play. Hansberry uses the characters to compare and contrast the difference in values between Mama's generation and Beneatha's. Mama's generation was that which migrated from the South to northern cities like Chicago, the setting of the play, in the early part of the twentieth-century. Beneatha's generation embraced Civil Rights, pan-Africanism, and later, would embrace Black Pride, which encouraged a singularly black aesthetic, as well as black nationalism.
Beneatha's generation had more access to education and opportunity than her mother's. This is exemplified not only by the erudite language that Beneatha uses, which befuddles her mother, but also by her experiments with different hobbies. For example, Beneatha announces that she will start guitar lessons, a pastime which makes no sense to either Mama or Ruth:
Mama: How come you done taken it in your mind to learn to play the guitar?
Beneatha: I just want to, that's all.
Mama: (Smiling) Lord, child, don't you know what to do with yourself? How long it going to be before you get tired of this now -- like you got tired of that little play-acting group you joined last year? (Looking at Ruth) And what was it the year before that?
Ruth: The horseback-riding club for which she bought that fifty-five dollar riding habit that's been hanging in the closet ever since!
Beneatha is defiant in spite of their trivialization of her efforts, repeatedly explaining her desire to try new things by saying, "I just want to." The phrase is simple and mundane, but expresses a powerful sense of agency that eludes both Mama and Ruth, neither of whom had the chance to simply do whatever they wanted due to being responsible for other people and for lack of opportunity. Because Mama probably spent much of her life being practical in order to care for her children, and arose from circumstances in which acting and horseback-riding were unavailable to black people, who had little to no leisure time, Beneatha's shifting interests are perceived as shiftlessness:
Mama: (To Beneatha) Why you got to flit so from one thing to another, baby?
Beneatha: (Sharply) I just want to learn to play the guitar. Is there anything wrong with that?
Mama: Ain't nobody trying to stop you. I just wonders sometimes why you has to flit so from one thing to another all the time...
Beneatha insists that she doesn't "flit," but is simply looking for different ways to express herself. This explanation is too abstract for Mama who asks, "What is it you want to express?" When Beneatha responds, "Me!" in anger, this elicits the laughter of Mama and Ruth and the frustration of Beneatha.
Self-expression requires one to have the time to sit and think about one's own needs and place in the world. Again, Mama and Ruth were never allowed this time. Moreover, one must be able to access the language required to express those needs. Some of this language is conceptual, derived from philosophy, the arts, and psychology. For example, when Beneatha describes her brother as "an elaborate neurotic," Mama tells her to hush. The order comes from a sense of knowing that Beneatha is insulting her brother's character, but also probably comes from Mama not knowing what Beneatha is talking about.
The main area in which Mama and Beneatha clash is in their acceptance of religion. Mama is a devout Christian. Beneatha, to her mother's outrage, pronounces herself an atheist. Whereas Beneatha's other strange ideas are met with tolerance, her declaration that God does not exist is unacceptable. Mama slaps her daughter and forces her to repeat, "In my mother's house there is still God." Mama follows this by saying, "There are some ideas we ain't going to have in this house. Not long as I am at the head of this family." Beneatha agrees to this rule in her mother's presence, then reasserts her atheism to Ruth once Mama is out of earshot.
By declaring herself the head of the family and violently rejecting Beneatha's atheism, Mama's words and gestures symbolize the elder generation's refusal to allow the younger to eviscerate old traditions. Christianity, though adopted during slavery, served as a source of strength to Mama's generation and those previous. Religion was one of few areas in which black people could find solace, community, and self-expression. To deny the existence of God is to deny the validity of those experiences.
In spite of their differences, both Mama and Beneatha reach a consensus of sorts at the end of the play in their agreement that the family should move to Clybourne Park, thereby integrating the white, segregationist community. This agreement signifies that, despite their generational and ideological differences, both really want the same things: both want the family to progress by moving to a better home, and both wish for black people to be equal and free.