What did Scout mean when she commented that Calpurnia "had a separate existence outside our household," and that she even had a "command of two languages" in Chapter 12 of To Kill a Mockingbird?
Before her visit to Calpurnia's church, Scout has only seen the one side of Calpurnia: In the Finch household, Cal is a teacher and role model for the children, and she speaks much differently than she does among her own people at First Purchase Church. She is well-educated for a black woman of the period, and she has taught her son, Zeebo, to read and write as well. They are among the few literate African American members of the church. She speaks Southern slang in the Finch home on occasion, especially when she is angry, but her language is much more proper there. With her own people, she speaks "nigger-talk" because "it'd be out of place" otherwise. Cal believes "It's not ladylike" to make it appear that she is "puttin' on airs."
"... folks don't like to have somebody around knowin' more than they do. It aggrevates 'em." (Chapter 12)
Cal chooses to deliberately lead a "modest double life" because it allows her to fit into both the white and black worlds of Maycomb: She is able to serve the Finches faithfully while maintaining her dignity and respect among her black friends.