Interesting here, to me a least, is that no-one has mentioned the styles that are collectively known as Rhythm and Blues. R&B seems to broadly spans the gap between out-and-out Soul and pure Blues. I've always placed artists such as Boby Bland and Z.Z. Hill in this area, though, of course, their material cuts right across the spectrum as a whole. If I may go slightly off the original question, I don't think that the mentality that deliberately refuses to accept certain songs or artists because they aren't whatever the definition says they should be is at all helpful or desirable. A lot of R&B gets played at Soul nights, and, of course, the Mod scene has always accepted a wide variety of tunes from Soul, R&B, Blues, Ska, Latin, 60s Beat etc., etc. Music is a continuum, not a series of clearly defined chunks, and there is great material to be heard at any event, no matter how is it advertised or marketed. So, I don't think it's all that important what niche you place Bobby or Z.Z. in: their music is wonderful, and that's all that matters.