A mockingbird symbolizes innocence. How is the symbolism of the mockingbird used to unite the two plot lines of Boo Radley and the trial of Tom Robinson? What do those two men represent in this society?

Think about the title, To Kill a Mockingbird, and remember Atticus' line where he reminds Scout and Jem that "it's a sin to kill a mockingbird." TKAM is all about prejudice and the differing forms, innocent (as with the children's perceptions of Arthur Radley) and ugly (witness the false accusation and ultimate death of Tom Robinson) that it can take. Arthur and Tom are both "mockingbirds" in that sense, because they are both kind, unassuming, and retiring - they bring nothing but pleasure to the people they know. Arthur's kindnesses toward the children are downplayed, but speak volumes about the true nature of this neighbourhood legend. Tom's kindness is toward Mayella Ewell. Because of their "otherness", however, both Tom and Arthur are viewed as dangerous, frightening. Arthur literally becomes "Boo", a boogie man, and Tom becomes that even more frightening figure, a black man with the audacity to show human kindness to a white woman. Thus the two men are connected, under the title, and their two stories share more than characters - they share the role of scapegoat for the ignorance and prejudice of this archetypal southern town.