The avoid note principle is slightly contentious, and sometimes confused with other principles.
You're right that it's about chord extensions that disturb the harmonic function of the chord. (Wiki's phrase "harmony implied by the chord root" is debatable. Chord roots don't imply harmony.)
It doesn't mean a note that needs to be avoided in any
melodic phrase on that chord.
The shorthand guide to what an avoid notes is is "any note a half-step above chord tone" (meaning triads in the first place).
That's why both dorian and lydian are considered to have none. The 2, 4, 6 and 7 of each mode are all a whole step above the triad tones. In all other modes, at least one of those notes is only a half-step above.
(When 7ths are added, then the root of maj7 chords becomes an avoid note, at least if high in the chord. Which is why, when a melody is the root note, a 6th chord will be used instead of a maj7.)
However, that shorthand view is a simplification.
Harmonic function - in both keys and modes (modal jazz) - brings other rules into play.
DORIAN & LYDIAN
So the ii chord in a major key is often said to be "dorian", but that's a misapplication of terminology. In practice it's "ii in Ionian" - if you need a modal term - but "ii in major" to be sensible about it. ;-)
As a ii chord, its job is to lead to V. The problem with the major 6th of the ii is that it's the leading tone of the key, a crucial chord tone on the V chord. So if you include it on the ii chord (add a B to Dm7 in C major) you're pre-empting the V (G7) - robbing the V of its role, confusing the different functions of each chord. Quite often in jazz harmony, the only significant difference between voicings of Dm7 and G7 is that C-B voice-leading move. (You could have Dm11-G9, which are all the same notes with the exception of C-B.)
For that reason, B would be considered an avoid note on the ii chord.
You might point out that surely the same reasoning would apply to Fmaj7 - because F can also lead to G7, shouldn't B be an avoid note there too? Maybe - except in jazz you almost never get Fmaj7 leading to G7. And if you did, the #11 (B) would probably be avoided.
But generally Fmaj7 is not used in that way, so the #11 can usually be added. It doesn't disrupt the IV function of the chord.
(And of course, Fmaj7 in C major is not really "lydian" in any useful sense.)
In modal harmony, different rules apply. Rather than "avoid notes", you have "character" notes, or "modal tensions".
The theory of modal harmony in jazz is debatable, but a good guide to common practice is that each mode has two possible types of chord. A "stable" chord - any bunch of notes
excluding the character note; and an "unstable" (secondary or contrasting) chord - any bunch of notes
including the character note.
As you'll probably guess, B is the character note of D dorian. As such - in that theory - it would be an avoid note on any stable D dorian chord. (But would be included on the contrast chord, still in D dorian mode.)
In lydian mode, the #11 is the character note, but seems to cause fewer problems as part of a stable modal chord - although a lot depends on the voicing, seeing as it forms a tritone with the root. In a case where primary and contrasting chords are used, it would be part of the contrasting chord.
LOCRIAN
Applying the shorthand theory to locrian mode, the avoid note is as wiki says: the b2 (b9). The 6th is OK, because it's a whole step above the 5th (b5 and b6).
Jazz chord-scale theory follows that principle, and states that any 9th on a locrian chord should be a major 9th - implying a mode of melodic minor.
(Eg B C# D E F G A for a Bm7b5 chord).
However - again, modal terms are not a lot of use in functional harmony. A Bm7b5 chord is normally used as ii in key of A minor, and one would need to consider whether adding a C# to that chord (major 3rd of the key) is really appropriate. (The b9, C, would still be avoided, however.)
Some jazz tunes do feature m7b5 chords used in ways other than ii in minor (or vii in major), and in those cases a major 9th may well be suitable.
And in modal harmony - as a mode in its own right - locrian doesn't really exist anyway! Forget about it!
Edited 3 time(s). Last edit at 07/17/2015 02:42AM by JonR. (
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