Aunt Alexandra's ideas about "trash" are seen early in the novel when she comes to stay with Atticus and the kids for a while. She takes it upon herself to begin teaching Scout that Finches are more respected members of society than most of her neighbors, and she "never let...
Aunt Alexandra's ideas about "trash" are seen early in the novel when she comes to stay with Atticus and the kids for a while. She takes it upon herself to begin teaching Scout that Finches are more respected members of society than most of her neighbors, and she "never let a chance escape her to point out the shortcomings of other tribal groups to the greater glory of our own" (chapter 13). She therefore teaches Scout of the shortcomings of "lesser" families all around them:
"All the Penfield women are flighty.” Everybody in Maycomb, it seemed, had a Streak: a Drinking Streak, a Gambling Streak, a Mean Streak, a Funny Streak. (Chapter 13)
Aunt Alexandra believes that such shortcomings are "hereditary" and cannot be overcome. She thus extends these thoughts to her feelings about poor families like the Cunninghams, telling Scout that young Walter is "trash" and that she will surely pick up "his habits and [learn] Lord-knows-what" from his association. Aunt Alexandra cannot distinguish between poor people who are hardworking members of society and people like Bob Ewell, who are poor and morally detestable. She feels that she must erect a solid wall between her family and families of lower socioeconomic standing.
Atticus, of course, believes in seeing the true character of a person and not their class standing in society. In fact, when Aunt Alexandra is commenting on various family "streaks," Atticus jokingly asks her,
Sister, when you stop to think about it, our generation’s practically the first in the Finch family not to marry its cousins. Would you say the Finches have an Incestuous Streak? (Chapter 13)
Atticus believes that people like Bob Ewell are trash because of the evidence of their character in how they treat others, and particularly society's most vulnerable, such as Tom Robinson. He teaches his children that wealth and "fine families" mean nothing if a person's heart is filled with ugliness—that is what makes a person "trash."