She is authoritative for one thing. This does put her on par with Atticus in bringing up the two kids, but being black her character also acts as a foil to Scout's character, teaching her the proper values in life.
And Valerie Smith in Black Feminist Theory and the Representation of the "Other" says that "Black women are employed, if not sacrificed, to humanize thier white superordinates, to teach them something about the content of their own subject positions" (1989, p. 375). However, Smith says this in relation to the portrayal of black women in relation to several films.
I wish I weren't so late to arrive at this great discussion. I agree that Calpurnia is not a simple character to place within the social hierarchy of Maycomb. In teaching the novel this semester, I have been prompted by the in-class and written statements of very perceptive students to think more about how she is positioned within the world of the novel. One student wrote the following, in a move toward deconstructing the conventional reading of the novel:
There is one major gap that is overlooked easily. Since Tom’s trial occupies most of the attention, it is easy to overlook one line by Miss Jean Louise. When the mad dog is coming through town, Calpurnia goes over to the Radley place to warn the inhabitants there. As she knocks on the front door and yells the news, Scout says, "She’s supposed to go around in back" (Lee 107). If this is the case, then for all Atticus’s polite attempts and agreements with Calpurnia, she is still required to follow the laws of segregation at his house.
I would add that the narrator herself seems more than a little conflicted about Calpurnia. When we first are told about Calpurnia as a character, we learn in a brief paragraph that she is simply the cook, a less than fully integrated member of the Finch household: “We lived on the main residential street in town -- Atticus, Jem and I, plus Calpunia our cook.” (That label does not hold up well, of course; as we later learn, she is much more than a cook to the family.) The more developed paragraph after this short one gives more detail on Calpurnia and is followed by an equally long, wholly unexpected paragraph on Scout’s dead mother. Calpurnia and Scout’s dead mother are strangely connected across the paragraph break, particularly through the contrasts of presence/absence and of remembering/not remembering. Scout says first of Calpurnia and then of her mother: “I had felt her tyrranical presence as long as I could remember. / Our mother died when I was two, so I never felt her absence.”
I don’t see Calpurnia as conforming to some common stereotype of black women, but I do think that Valerie Smith’s critical analysis may be applied meaningfully to this character and to her place within the novel. Calpurnia is positioned as an “Other” in multiple ways, and she is used in the story to bring into focus the identify (or subject position, if you will) of the immediate Finch family: “Atticus, Jem and I, plus Calpunia our cook.”
When I teach this book to my students, we always talk about the social hierarchy of Maycomb, and they never know where to put Calpurnia--does she go at the bottom with the rest of the blacks or is she elevated because of her status in Atticus' home?
I think superficially Lee wants Calpurnia to seems a stereotypical black woman--she serves a white family, some of her language, even in the Finch house, is that of the black community. But it is through a reflection of Atticus' behavior that we come to see her as more than a stereotype. It would have been very easy for Lee to make Calpurnia a "Mammy" type character, but the respect Atticus shows her and the authority he gives her and the kindness with which he treats her brings her above that stereotype.
If a reader just wants to see Calpurnia as another black serving a rich white family, I think a reader is allowed to do so, but I think that reader would be missing a valuable point in Lee's book. She chose to make Calpurnia black for a reason (even though it was the norm at the time). Atticus could have hired a white person to care for the kids--but Lee had him hire a black woman. And my guess is that Atticus paid her just as much as he would a white woman.
At the same time, remember that we also see Calpurnia teaching her own community something when she brings the children to First Purchase Church. One of the parishioners became very irate with Calpurnia for having brought white children to their church, however Calpurnia defends them and I think at that moment is showing her own community something.
Furthermore, Scout also mentions at this time how she noticed that Calpurnia's language had changed all of a sudden when she responded to the irate woman, noticing that Calpurnia was now speaking like the other blacks citizens Scout had ever met rather than the way Scout and her family spoke. If Calpurnia was portrayed as the stereotype of a black woman, then I don't think she would be able to switch "code" in this way, from one form of spoken word to another.