Some more of the explination about dispensing with the notes runs along the
line that -
The root isn't essential to the chord. It is probably being played by some
body else, the base player. Alternativly the progression is so well known,
like a blues, it can be dispensed with.
The 5th is always implied in a chord and so not required. It is the same
interval for both a minor and a major chord. Bar more unusual chords with
and altered 5th it's always the same so people will hear it even if it isn't
there.
If you don't believe that the 5th is strong enough to be done away with then
grab some one weather musical or not and play a note for them. Then ask them
to sing another note. You will probably find that they sing the 5th.
All the additional notes such as 9th, 11th, 13th, are just flavorings for
the chord. They give it some texture but are not essential.
The important notes are the third which diffines major or minor. And the 7th
which diffines the chord type eg dominant 7th, Maj 7th, min 7th.
As I said above a good place to start is looking at dom 7th tri tones in a
12 bar blues. The tones for the chords in an A blues are
A7 - C# and G
D7 - F# and C
E7 - G# and D
When you play them there is very little movement between the chords. On a
guitar you could play the A7 tones with the G on the 3rd string 5th fret and
the C# on the 4th string 6th fret. To play the D7 you move 1 fret down or
1/2 a tone on a piano. And the E7 is 1 fret or 1/2 a tone up from the A7.
The two tones are an equal distance apart so that you are just inverting the
chord/tone when you play it.
This then explains why flat 5 substitutions work so well. This is when you
are about to change from a dom 7th chord to a dom 7th chord a 4th away from
it you can substitute a flat 5 chord as a lead in. eg in a blues prog.
A7 Eb7 | D7 | A7 |A7 Eb7 | D7 ......
The tri-tones in the A7 and the Eb7 are the same.
A7 - A C# E G
Eb7 - Eb G Bb Db/C#
So there is no movement in the 3rd and 7th. It makes a realy good substitution.
See ya.
Data is not information,
Information is not knowlegde,
Knowledge is not wisdom. Anon.