A rhetorical question is one a speaker asks without expecting the audience to answer. Think of questions-not-questions like:

Are you serious?

What were you thinking?

Do you think I was born yesterday?

(And that's just pulling from the great list of "Rhetorical Questions Every Parent Asks.")

The point is to get the audience thinking or to demonstrate that there's only one correct answer, which the speaker isn't even going to tell you because it is so obvious.

Twenty-four of the 84 sentences in this speech are rhetorical questions. That's nearly 30 percent…which is a sizable chunk. In fact, the entire first paragraph is made up of rhetorical questions:

Fellow citizens, pardon me, and allow me to ask, why am I called upon to speak here today? What have I or those I represent to do with your national independence? Are the great principles of political freedom and of natural justice, embodied in that Declaration of Independence, extended to us? And am I, therefore, called upon to bring our humble offering to the national altar, and to confess the benefits, and express devout gratitude for the blessings resulting from your independence to us? (1-4)

Then, Douglass uses rhetorical questions to set up all the points he says he's not going to argue:

Would you have me argue that man is entitled to liberty? That he is the rightful owner of his own body? You have already declared it. Must I argue the wrongfulness of slavery? Is that a question for republicans? Is it to be settled by the rules of logic and argumentation, as a matter beset with great difficulty, involving a doubtful application of the principle of justice, hard to understand? How should I look today in the presence of Americans, dividing and subdividing a discourse, to show that men have a natural right to freedom, speaking of it relatively and positively, negatively and affirmatively? (54-60)

If anyone in the audience isn't paying attention by this point, it's not Douglass' fault.

Douglass isn't alone, though. Early American orators loved the rhetorical question, and he might have learned this technique from The Columbian Orator, as well as from speakers he worked with.