Sometimes confirm and affirm can mean the same thing, but there are times when you need to use affirm rather than confirm. I think the second to last sentence is the best one to explain the difference: "I confirmed/affirmed his doubts about her innocence." "I confirmed his doubts doubts about her innocence" and "I affirmed his doubts about her innocence" both can mean "I validated the fact that he has doubts about her innocence." But to say "I affirmed his doubts about her innocence" can also mean "I gave reasons why his doubts were valid," such as maybe providing eyewitness testimony about "her." Affirm also implies the person doing the affirming is in a position to give first-hand evidence. So if you went to someone else who affirmed that his doubts were valid (such as an eyewitness to her actions), then you would use "confirmed" in that sentence; such as, "I confirmed (with an eyewitness that) his doubts about her innocence (were valid)." If you come across the sentence, "I affirmed his doubts about her innocence" in order to tell whether the speaker as affirming the fact that he had doubts, or affirming that his doubts about her were valid, you would need to see the sentence in context. Also note that this is a very subtle point, and the difference in usage often gets blurred in common speech. If you're reading a formal essay or court transcript, the two words are MUCH more likely to be used in the correct context than in informal speech. For example, if a reporter is doing a street interview with a member of the public on a high-profile court case, there's a decent chance the interviewee is speaking informally and might use the word "confirm," when really he means "affirm" or vice-versa.