How does douglass use the word choice and literary references to confirm his credibility ?

it seemed that Douglass used a high level of benevolent vocabulary when he described Mrs Auld and depravity when he described some qualities that were not innate to her. This alteration could have made this massage more convincing or credible to those people in a powerful position. What is more, through his writing he showed that slaves did not lack of intelligence. 

c.to compare several aspects of the tragedy to other worldwide tragedies