What are both the connotative and denotative meanings of Atticus' statement that "this case is as simple as black and white" in Harper Lee's To Kill a Mockingbird?
The term denotative meaning refers to the literal meanings of words. Literally, the idiom "black and white" has come to mean that things are so simplistic, they are obvious; they are unambiguous (Collins Thesaurus of the English Language).
Atticus calls Tom Robinson's case as "simple as black and white" in his closing remarks to the jury at the trial. From there, he continues to explain why the case is so simple. It's simple because "the state has not produced one iota of medical evidence" proving that the crime Robinson is being "charged with ever took place" (Ch. 20). The only evidence used in the trial was the testimonies of the alleged victim and her father. Since no concrete evidence has been produced, as Atticus states, "[T]his case should never have come to trial" (Ch. 20). Hence, the case is "black and white," meaning simplistic and unambiguous, since not a shred of concrete evidence has been produced to prove a crime was even committed, and with no proof of crime, there should be no trial.
The term connotative meaning refers to the positive and negative emotions usually associated with words that can give words meanings beyond their literal meanings. The phrase "simple as black and white" can also be interpreted as referring to racial tensions that are a result of racial discrimination. Atticus is using the phrase "simple as black and white" to subtly point out that the only reason why Robinson's case was even brought to trial is because a white woman and her father accused a black man of a crime. Due to racial prejudices, white folks have had a tendency to discriminately believe that all black folks are by nature criminals. We see this prejudiced belief expressed among the women in Aunt Alexandra's missionary circle such as when Mrs. Farrow reports to the circle the comment she recently made to Brother Hutson:
... looks like we're fighting a losing battle, a losing battle. ... We can educate 'em till we're blue in the face, we can try till we drop to make Christians out of 'em, but there's no lady safe in her bed these nights. (Ch. 24)
Since Atticus is aware that most white folks in Maycomb judge black folks to be inferior, he is also aware that Robinson will inevitably lose the case because he knows the jury will convict Robinson simply based on the jury members' racial prejudices, not on the evidence. Therefore, in saying that the "case is as simple as black and white," Atticus is implying that the case boils down to white men's racial prejudices against an innocent black man. Hence, Atticus is giving the phrase "black and white" non-literal negative connotations by relating the phrase to racial tensions and prejudices.