The way Frederick Douglass writes in his autobiography, Narrative of the Life of an American Slave, is largely influenced by the fact that he is writing mainly for a white readership, and not only of abolitionists, but also of those who do have to be persuaded of the evil of slavery and the intelligence and humanity of blacks. If he were writing for a black audience, it might not be necessary for him to prove the evil of slavery at all; he could begin by assuming the evil of slavery as his and his readers' shared premise, and go on from there, probably to discuss how best to bring about its abolition; which would make it a very different book. Since Douglass is writing for a white readership, he writes in such a way that the reader doesn't know when he is leading into an argument until he is making it.
Much of what he writes is in refutation, directly or by example, of the views and arguments of the advocates of slavery. For example, advocates of slavery would often point out that slaves themselves often praised the kindness of their masters. Douglass refutes this first by example: He segues from the wealth of Colonel Lloyd, to the number of Col. Lloyd's slaves, to the fact that because of this great number, Col. Lloyd did not recognize one of his won slaves when he met him on the road, and the slave, not knowing he was talking to his master, answered Col. Lloyd's questions honestly, telling him that he was mistreated, and in consequence was separated from his family and sold into Georgia(p. 1946-47).
Douglass then goes from the specific incident to the general situation, refuting the slavery-advocates' argument by explanation--"The frequency of [the spies on behalf of the masters] has had the effect to establish among the slaves the maxim, that a still tongue makes a wise head." Douglass makes the explanation stronger and more convincing by putting the example that proves it before it, and gets past at least some of his readers' intellectual "defenses" by segueing into the subject of why slaves praise their masters without showing his readers where he's going until he's there.
Similarly, he explains why slaves sang. Advocates of slavery often would point to the fact that slaves frequently sang, to argue that they were happy, therefore they were not being mistreated, and their enslavement was no hardship to them. The slavery-advocates argued, furthermore, that this singing showed that blacks were essentially happy and content by nature, with the implication that nothing that whites did to them could hurt them, and that they did not have the same human nature that whites did.
Douglass refutes this in the same manner with which he refuted the argument concerning the fact of slaves saying the were well-treated: He starts by segueing into the concrete example--from the farm that the slaves called the Great House Farm, to what the slaves did and felt who were sent to the Great House Farm, to their singing, to the reasons why they sang, to the general explanation--arguing against the slavery-advocates who claimed that their singing was a sign of happiness.
He writes: "The songs of the slave represent the sorrows of his heart; and he is relieved by them, only as an aching heart is relieved by its tears." Then he goes to his own experience, but since he is trying to communicate, not only his experience, but his very humanity, to whites, his next two sentences are ones that express experience that whites could also relate to, that might have happened to them: "I have often sung to drown my sorrow, but seldom to express my happiness."
His next sentence refers to his experience as a slave, but the sentence after that raises an image of a man who might well be white, "a man cast away on a desolate island," singing to relieve his misery, as the slave does. Douglass uses a hypothetical man that it would be easier for white readers of his time to relate to. He does this to make it easier for them to empathize with the slaves and comprehend what they might be feeling, in order to help his readers see the slaves' humanity, as he demolishes the argument that slaves sing out of happiness. (p. 1945)
The Autobiography frequently echoes, and subverts, the traditional features of traditional nineteenth-century autobiography and fiction. It starts with the few statistics Douglass has about his birth--i.e., where he was born, but not when. Autobiographies of the time often started with where the author was born, and his or her birthday. Douglass is subverting
that convention, by describing his lack of knowledge of when he was born, and at the same time, describing, beginning with the second sentence, one of the ways in which slavery denies slaves
the things that whites take for granted--i.e., knowledge of when
they were born and who their parents are.