How does the illiteracy of African-Americans in To Kill a Mockingbird contribute to the novel's themes?
Lee addresses the issue of education, and more specifically, literacy, in several parts of the novel. In regards to race, Lee includes the incident in Chapter 12 when Calpurnia brings the children to church, and Scout and Jem are fascinated by the manner in which the church members sing their songs (not by words in a hymnbook). When they ask Cal about this, she explains to the children that most of the church members do not know how to read; so they have to repeat what is modeled for them in order to sing. Cal tells Jem and Scout that she taught her own son to read by borrowing books from her boss years ago. This conversation illustrates several truths. First, Lee proves that if humans, no matter what race, want to be literate, they will do so, even if it means having to develop ingenious ways to accomplish their goal. Secondly, Lee demonstrates that in order for someone to be moral and decent, he or she does not necessarily have to be literate. Tom Robinson and other members of the church are the epitome of this.
On a more general note, the author subtly reveals the fact that those in power often try to use illiteracy as a means of controlling others. They know that it is dangerous for someone whom they desire to control to "think" too much.