Why don’t we call the major sixth a “blue note?” From the earliest days of jazz and blues, it’s been a basic part of the blues melodic vocabulary. Here’s a perfect example - check out Illinois Jacquet’s opening phrase. It’s an archetypal blues lick, 5-6-1-3-1-3:
I’d argue that in terms of traditional blues vocabulary, the major sixth is just as important as the the flat seven or flat five.
Here’s Bessie Smith’s 1925 rendition of “Yellow Dog Blues” (W. C. Handy, 1915). You’ll hear major sixth licks all through it:
There are countless other examples of the major sixth in blues licks, from all eras of jazz and blues.
Maybe we should try to better define our terms. What exactly is a “blue note,” anyway? Merriam-Webster cites the first use of the term “blue note” as 1919; Dictionary.com says it dates from 1925-1930.
Pretty much everyone agrees that the term “blue note” refers to a flat third or flat seventh, often in a context that is otherwise major-key. For about the last 70 years or so, one could include the flat fifth as well.
As I see it, the term was originally coined to describe the use of notes that contradicted the simple diatonic vocabulary of most early popular music. It’s an ethnocentric term, describing a Southern, mostly African American melodic usage that was at the time (c. 1919) heard by most mainstream-culture Northerners as unusual and exotic.
The terms “blue notes” and “blues scales” don’t go very far in actually defining the language of blues and jazz. They are overly-limiting concepts (though that limitation can be helpful to beginners); also, these terms say nothing about rhythm. Musicians, and especially educators, would do better to think of blues usage in terms of melodic vocabulary (licks).
True, the “blues scale” can be a useful teaching tool. When I help beginners learn to improvise, I nearly always start by having them experiment with a “minor blues scale” (1-b3-4-b5-5-b7-1), while I play a basic 12-bar progression on piano. They usually sound good right away, which gives them confidence. In addition, they usually end up finding some traditional licks in playing around with the blues scale - and that’s a good thing. Fortunately, most people today have heard plenty of blues, even if they didn’t know that’s what they were hearing, and they will intuitively draw on it.
But the next step is to tell them that actually, any note could work, depending how it is used.
The “major blues scale” (1-2-b3-3-5-6-1) is a useful concept too - again, because it draws students into traditional licks, this time including the major third and major sixth. You can’t use this scale over the entire progression like you can the minor blues scale, because the major third in this scale doesn’t work so well over the IVdom chord (e.g., playing the note E natural over the F7 in a C blues). Also, the “major blues scale” omits the flat seventh. And anyway, dwelling on a scalar approach to improvising is kind of going down the wrong road, I think - not the best way to get students to play melodically.
Getting back to the major sixth - I’d speculate that its use in traditional blues licks traces back to 19th-century hymns - consider “Amazing Grace” (the words were set to its present melody in 1835), for example - and before that, back to English/Irish folk music (e.g., “Londonderry Air,” c. 1792). I suppose you could call that usage “major pentatonic,” if you subscribe to the oversimplistic theory that pentatonic scales are somehow an Ur-form of world music.
In terms of defining the vocabulary, some notes are bluer than others. The flat third is the bluest (maybe we should call it the flat/major third, or bent third); after that the flat seventh, flat fifth, and major sixth, then maybe the second and fourth. The performance practice of bending notes (pretty much any note) is a separate, but related, element in jazz and blues vocabulary. It can turn any note “blue” - think Johnny Hodges or Jimi Hendrix.
In a due-diligence internet search, I ran across an article by Hans Weisethaunet, Is There Such a Thing as the “Blue Note”? It’s worth reading (I agree with some, not all, of what he has to say). Weisethaunet concludes that:
…there is no such thing as the blue note, the ‘item’ of musicology. There is no such thing as the ‘blue note’ as a strange or ‘out of tune’ third or seventh (apart from in the theories and ideologies of a few musicologists). Rather than thinking of ‘blue notes’ as pitches being out of tune, ‘blue harmony’ creates a space for the play of identity in music performance...My perspective here is not that of a musicologist, but of a player and teacher. My point in this post is simply that blues and jazz are best thought of as a matter of tradition, vocabulary, and creative evolution over time. The terms “blue note” and “blues scale” are useful and descriptive, and can be utilized as teaching tools, but the blues/jazz tradition is far more than these simplistic concepts, and students should be made aware of that early on.
If you want to teach a student what constitutes a blues vocabulary, you couldn't do much better than to have them listen to the two videos above, as a start, then check out another thousand classic blues on Youtube. Don't forget this one; the melody opens with a major sixth lick, right after the intro: