How is fear one of Harper Lee's themes in To Kill a Mockingbird?
--Concerning Mayella's motivation to accuse Tom Robinson.
--Concerning the jury's decision to make Tom guilty of a crime he did not commit.
Considering the distinct possibility that Bob Ewell may have beaten Mayella often and even may have had some sort of sexual relationship with his own daughter, Mayella must have lived in fear for most of her life. Atticus had already established the likelihood that Bob had beaten her before. She tells Atticus that Bob
"... does tollable--'cept when--"
"... Except when he's drinking?" asked Atticus so gently that Mayella nodded.
During his testimony, Tom reveals that Mayella had told him that
"... she never kissed a grown man before. She says what her papa do don't count."
These two bits of information reveal an even more sinister side of Bob than Scout has revealed during her narration. Assuming that Bob had already beaten Mayella after he discovered her hugging and kissing Tom, she must have known that further physical abuse awaited her if she went against Bob's claim that Tom had raped her. Mayella certainly feared her father more than she liked Tom, and for her, it was an easy decision to bide by her father's wishes.
As for the jury's decision to overlook the fact that Tom's disability prevented him from causing Mayella's injuries, the white men of the jury were not about to change the age-old social dictum that decreed that a black man's word was never to be taken over that of a white man's. Such an action might disrupt the status quo that kept the Negro on the bottom of the social ladder. The fear of the black man is best illustrated when one of the Maycomb citizens worries that black men
"... c'n go loose and rape up the countryside for all of 'em who run this county care."
At the Missionary Circle meeting, Mrs. Farrow describes her own fear of Negroes.
"We can educate 'em till we're blue in the face... but there's no lady safe in her bed these nights."
Fear exists in other ways in Maycomb. People fear Boo Radley and they fear outsiders, and the fear of the unknown is a powerful one. But the ruling fear in Maycomb is that one day, the black man may rise up to become equal to the white people of the community.