The "blue note" and tritone substitution
I've been trying to figure out what the "blue note" is according to musical theory, and am a bit confused. The term seems to be used for the flattened third, fifth and seventh of a parent major scale, but some places it's claimed that the flat fifth (i.e. the tritone) is the "blue note". I've also seen that in a minor pentatonic scale the tritone is added as the blue note to make it a blues scale, while in a major pentatonic, the note added is the minor (flat) third, which makes sense since it's the same note in the parent major scale. I also notice that chromatic movements is present in many blues licks and phrases, where the flattened notes creates a tension that is resolved upwards or downwards. One particular example is the chromatic root migration created by tritone substitution for the V chord in a ii-V-I progression (giving ii-bii-I). I've got a feeling that all of this is related, and is the key to what makes the blues tonality, but can't find any explicit discussion and explanation of this relation. Can anyone round here enlighten me? :roll:
Yes, it's all related.
Which one is the "blue note" depends on your perspective - I was taught it was the b5 only, but when I started jamming with old blues guys they'd call the blue note whatever note happened to make it sound like the blues - even if it was in key, like the 6th.
According to the Harvard Dictionary of music, it's sometimes applied to the 3rd and 7th, whether they're natural or flat. And since blues isn't a classical form, you won't get much of a better answer - there is no "traditional" theory, since most of the originators of the style were doing it by ear.
Chromatic migration is common in the blues. Typically, if you're on a I or a IV chord, you're playing a note that's a half step away from a chord tone, and then migrating into a chord tone. So if you're doing blues in A, using the Am pentatonic, you might play C (which is in the scale) and then C# (which isn't) over the I chord. When you get to the IV, you might do the same lick moving from F to F# - neither of which are in the scale. This disonance/resolution is typical of blues.
Once you get to the V chord it's a different story. The job of V is to add tension that's going to be resolved when you move to I - you don't want to reduce that tenison prematurely. So you don't play G# over the E7 - you play G, and use the difference to create melodic disonance. Harmonic disonance can be created by playing the V chord a half step off, and "resolving" it into key (it's not a full resolution, because there's still tritone tension inside the chord). So you could play F7->E7 ("Stormy Monday" uses this). You can also add altered notes, like playing an E7#9... and you can combine the two, playing F7#9 -> E7#9; that's often done to dress up minor key blues, like "Summertime".
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Thanks for your answer, it cleared up the picture a little. I guess part of the problem is that the blues is a fusion of African music and Western music and instruments, and that the combination of western equal tempered instruments and african tonality is difficult to describe by the "rules" of our harmony theory (though the actual harmonisation of the music is possible because of the equal temperament!) ;)
Found a great and interesting article discussing the blue note here, (in the file blue-note-artikkel.pdf). I wonder if it's a coincidence that the author is Norwegian like myself, maybe it's some national character that make us speculate on these matters? :wink:
Short days and long nights. :D
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Good set of papers from Oslo University. Thanks.