12 Years a Slave is just such an oral account. Though Northup was literate, his autobiography was written by David Wilson, a white lawyer and state legislator from Glens Falls, New York. While the incidents in Northup's life have been corroborated by legal documents and much research, Andrews points out that the impact of the autobiography—its sense of truth—is actually based in no small part on the fact that it is not told by Northup, but by Wilson, who had already written two books of local history. Because he was experienced, Andrews says, Wilson's "fictionalizing … does not call attention to itself so much" as other slave narratives, which tend to be steeped in a sentimental tradition "that often discomfits and annoys 20th-century critics." Northup's autobiography feels less like fiction, in other words, because its writer is so experienced with fiction. Similarly, McQueen's film feels true because it is so good at manipulating our sense of accuracy. The first sex scene, for example, speaks to our post-Freud, post-sexual-revolution belief that, isolated for 12 years far from home, Northup would be bound to have some sort of sexual encounters, even if (especially if?) he does not discuss them in his autobiography.
The difference between book and movie, then, isn't that one is true and the other false, but rather that the tropes and tactics they use to create a feeling of truth are different. The autobiography, for instance, actually includes many legal documents as appendices. It also features lengthy descriptions of the methods of cotton farming. No doubt this dispassionate, minute accounting of detail was meant to show Northup's knowledge of the regions where he stayed, and so validate the truth of his account. To modern readers, though, the touristy attention to local customs can make Northup sound more like a traveling reporter than like a man who is himself in bondage. Some anthropological asides are even more jarring; in one case, Northup refers to a slave rebel named Lew Cheney as "a shrewd, cunning negro, more intelligent than the generality of his race." That description would sound condescending and prejudiced if a white man wrote it. Which, of course, a white man named David Wilson did.
A story about slavery, a real, horrible crime, inevitably involves an appeal to reality—the story has to seem accurate if it is to be accepted as true. But that seeming accuracy requires artifice and fiction—a cool distance in one case, an acknowledgement of sexuality in another. And then, even with the best will in the world, there are bound to be mistakes and discrepancies, as with Mistress Epps's plea for murder transforming into Patsey's wish for death. Given the difficulties and contradictions, one might conclude that it would be better to openly acknowledge fiction. From this perspective, Django Unchained, which deliberately treats slavery as genre, or Octavia Butler's Kindred, which acknowledges the role of the present in shaping the past through a fantasy time-travel narrative, are, more true than 12 Years a Slave or Glory precisely because they do not make a claim to historical accuracy. We can't "actually witness … American slavery" on film or in a book. You can only experience it by experiencing it. Pretending otherwise is presumptuous.
But refusing to try to recapture the experience and instead deciding to, say, treat slavery as a genre Western, can be presumptuous in its own way as well. The writers of the original slave narratives knew that to end injustice, you must first acknowledge that injustice exists. Accurate stories about slavery—or, more precisely, stories that carried the conviction of accuracy, were vital to the abolitionist cause.
And, for that matter, they're still vital. Outright lies about slavery and its aftermath, from Birth of a Nation to Gone With the Wind, have defaced American cinema for a long time. To go forward more honestly, we need accounts of our past that, like the slave narratives themselves, use accuracy and art in the interest of being more true. That's what McQueen, Ejiofor, and the rest of the cast and crew are trying to do in 12 Years a Slave. Pointing out the complexity of the task is not meant to belittle their attempt, but to honor it.