Aunt Alexandra has very rigid ideas about what constitutes good breeding and respectable family. She is of the opinion that having an old, recognized family line from a well-established area is of the utmost importance. She behaves as though this factor alone should be sufficient to confer respectability and virtue on a person. She tries to instil this belief in hereditary values in Scout and Jem, as well as related ideas about maintaining a façade of social respectability by being genteel and dressing and behaving appropriately at all times. She also thinks that being of a good family background prevents one from mixing with those who are socially inferior. As Scout observes, ‘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)
Aunt Alexandra, then, places a premium on the value of heredity. However, her brother Atticus does not. When she finds out that he has been telling the children some less respectable, more lurid details about their family, such as the madness of Cousin Joshua, she is outraged. She tries to get him to impress the overriding importance of their family background on the children, and the fact that they are meant to be very respectable and dignified. However, he is very awkward in doing this and fails miserably, as he does not hold such beliefs himself. That is why he tells the children to forget it.
For Atticus, true breeding and respectability has little – if anything – to do with heredity. Rather, it lies in individual conduct. If a person is courteous, restrained, considerate and tolerant towards others, and has a proper sense of justice and morality unfettered by any kind of prejudice, that is what matters. I would say that Atticus is certainly much more in the right than Alexandra, who is much too preoccupied with family background and social class. She tends to see divisions between people whereas Atticus doesn’t. However, both Atticus and Alexandra coincide in their belief that a person must always act with civility and dignity. So, Alexandra is not entirely in the wrong.