This conversation between Scout, Jem, and Calpurnia occurs after the children go with Calpurnia to her church one Sunday. They are surprised to hear Calpurnia using the same language and slang that the other less-educated African Americans use. The children ask her why she speaks that way around them, when she knows it isn't the correct way. Calpurnia's response has two reason. The first reason she presents very directly, "...in the first place I'm black..." The second reason is more involved. She tells the children that it isn't always necessary to tell all you know. Speaking the way that "white people" do in her own church would make others think she was "putting on airs," trying to show off that she knew better than others. It isn't her place to make others feel badly for not knowing what she knows. It always isn't her place to try to teach them something they don't want to learn. Sometimes, its best to just be quiet. (Chapter 12)
This conversation is especially crucial for Scout. Up to this point in the novel, Scout has been very impetuous with her speech. She likes to let others know what she knows, and she makes others feel badly by pointing out their ignorance (such as on her first day of school). Calpurnia's lesson is one that Scout needs to learn.
Towards the end of Chapter 12, Jem and Scout are intrigued at the way Calpurnia speaks differently to her community members at church than she does around the house. Scout casually asks Calpurnia why she talks "nigger-talk" to the folks in her community when she knows that it is incorrect. Cal explains to Scout that it would be out of place for her talk like white people in front her black friends. She says, "They'd think I was puttin' on airs to beat Moses" (Lee 77). Calpurnia also tells Scout that it is not ladylike to make herself seem more esteemed than others. Cal then explains to Scout that it aggravates people when someone knows more than they do. Instead of trying to showcase her excellent English by articulating each word, Cal finds it better to speak like the rest of her community members so she doesn't upset them.