quote: Earlier than that it simply meant "an incorrect or off-pitch note." So it's easy to see how the secondary sense of the word developed - from a theoretically "wrong" note to a perfectly acceptable one.

Lighter: In another thread (Earliest jazzers how blues-interested?), Joseph Scott argued against that, because the earliest evidence of the use of the expression "blue note" is from several years after the earliest evidence of the idea of "blues" music.

I'm not convinced. I think a slang term can exist for a long time before it appears in print, especially if it describes part of a musical form practiced by a rural culture of a poor and oppressed minority, a form that hadn't yet come to the attention of the mainstream. And I think it's more plausible that the term "blue note" came first. It sounds like you agree. If so, do you have any evidence?

The Yates article also seems to agree with that order, suggesting that the blue note was something from an African scale that didn't appear to fit into the European scale, i.e. not a blue note simply because it was used in the blues style.