From John McWhorter at The New Republic:
Barack Obama’s inaugural address was the first in a long time to resound powerfully enough to be worthy of marble. However, it was the first in the 220-year history of the custom in another way: its seasoning of black cadence. This was even more exhilarating in that the cadence played an integral part in the power of the oration.
Black English is a matter not just of slang, but of sentence structure and sound (why you can tell most black people’s race over the phone, which is proven in studies). Some blacks use all three; Obama is one of the many who wields mostly the sound. Listen to the way he often ends sentences on a higher pitch than, say, Tom Brokaw would, with that preacherly hang-in-the-air. Or the way he often pronounces “history” as “historih,” “ability” as “abilitih.” His rendition of the word responsibility was indicative: with a cadence typical of Black English, capped by a final “ih.” No President has ever intoned sentences in this way, because they were not black.