Atticus Finch shows Scout the lack of absolutes in the law when he first speaks with her in part one. There, he explains the equal rights of Tom Robinson, despite the town's castigation of Atticus for "defending a nigger."
Scout first encounters a taste of moral "grey areas" during this section of the book -- She begins to understand that one must act according to one's own system of values, rather than abiding by popular opinion, or at times, even the law. Good and bad, black and white, and right and wrong are prevailing themes throughout this novel.
Atticus has many serious talks with Scout, yet the most important discussion and lesson in Part One of the book concerning the law occurs in Chapter 9. Scout asks her father, "Do you defend niggers, Atticus?" (Chap 9). Atticus goes on to explain to Scout that even though the town believes he shouldn't defend Tom Robinson because the town believes he is a "nigger," Tom is a person.
Atticus teaches his daughter that he must follow his heart and stand up for what is right even though the battle appears futile. Many times, what appears as black and white may not be the issue. One must act from one's beliefs and morals even if it is unpopular such as defending Tom Robinson in a losing battle.
Atticus teaches Scout that the law is not always back and white after she inquires Atticus to whether he defends niggers or not. Atticus explains to Scout that it is important to follow what you believe in despite who disagrees with you. Atticus tries to teach his daughter hat people should not be judged by the colour of their skin and even when times are hard and the odds are against you, it is vital to stick with your attitudes and values.