The Rev. Gary Davis? He worked both sides of the street. But the "blues" is sort of a postwar marketing construct, I think. When Robert Johnson was selling his soul to the Devil, they called music targeted to black markets "race records," African Americans and lots of white Americans too distinguished between sacred and secular music, but there wasn't a thing identifiable as "the blues." Jazz musicians were playing blue notes, flatted fifths and sevenths and that sort of thing, pretty much from the get go; Louis Armstrong not least among them. He also backed practically every important woman "blues" singer of the 20s including Bessie Smith; I have a six disc set of that work which is now rather hard to find. Charlie Parker's work is very bluesy. And (like jazz musicians) "blues" musicians played every which kind of thing; I was just listening yesterday to a Leadbelly recording and noticing that he was playing what would normally be identified as "country" music on a good many of the cuts. Also many of them played a lot of sacred music, as did Blind Willie Johnson and Rev. Gary Davis.
As to whether we could have had R&B or rock without the blues, gospel, and/or spirituals, I'm not sure what the point of the discussion is. Counterfactual history has its place ("was Stalin necessary?" and that sort of thing), but there has to be some point or you run into the problem Quine posed with his joke about the truth value of the following two sentences: "If Julius Caesar was commanding in Vietnam, he would have used the atom bomb;" "If Julius Caesar was commanding in Vietnam, he would have used catapults." How can you tell? As it played out in the real world, rock and R&B originated in blues and gospel. If there had not been blues and gospel but something else, would there have been Sam Cooke or Elvis Presley? What would count as an answer, and why would you want to know?
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