Hi Ian,
I am a Jazz guitar teacher, so maybe i can help you a little.

You use the modes for two things.
1.) To play the right notes
2.) To choose from (if the possibility is given) the moods that suite your needs.

ad 1)
If you have a dominant chord with "straight" (non-altered) notes, you usually (there are other possibilities too) play mixolydian over it.
The scale has: 1, 2/9, 3, 4/11, 5, 6/13, b7. That`s why you get only straight tensions like 9, 11 and 13. Because they are in the scale. So you can play G mixo over these chords: G7, G9, G11 (G9sus4), G13, and combinations.

Now you can and should use all of these notes. The important thing is, there are better and worse notes. The better notes are always the chord tones (meaning 1, 3, 5, b7). There are also better (and now I miss the englisch term for this) times to play those notes or the non-so good ones. the better times are: 1,2,3,4. The worse are 1+, 2+, 3+, 4+ (if you count in eights).

Now a simple but effective rule to start with would be:
Play the good notes on the good times. So play the chord tones on the beats and the other scale tones or chromatics on the offbeats. (This is of course not always true, but very common and very good and easy to start with)
You ought to land on a chord tone, that`s when you end your line you should be on 1, 3, 5 or b7 whatever time youre on at that moment (beat or offbeat)

Learn the arpeggios (Chord tones played in order), not to play them up and down, but to know where the chord tones are. So when you`re on the b-string you have to be able to quickly find the nearest chord note (on the b-string or adjacent string, don`t start from low E-string just because you only now the arpeggio from there)

Now G-mixo is the same scale as Cmajor, and D-dorian and E-phrygian and so on. The difference lays in the focus of the notes you play and when you play em. For a C major chord you can also play all the notes of the C major scale (just as for the G7 chord), but you focus on the Cmaj7 chord tones (C,E,G,B = 1,3,5,maj7). See? Now your lines will sound completely differnt than on the G7 chord with the G7 chord tones focused. You wouldn`t want to play a C there on beat 1, since it`s not a chord tone. As a matter of fact it`s the 4th of G, and therefor the "Avoid-Note", because it lays just beneath the 3rd of the G7 chord ("B).

In mixo mode you have to watch out the sus or 11 chord. Here the 3rd is ommited, therefore you shouldnt land on it, but instead use the 4th (which is usually the avoid note in mixo). So you could say there are actually two mixo modes. The one with the 3rd focused and the one with the 4th focused (only when you play sus chord. Like Herbie Hancocks "Mayden Voyage" if I remember right.)

As a good player one should be able to hear the chord changes in your solos even if the band would stop and you keep on playing alone. Because you focus on the chord tones of each chord.

ad 2)
If you compose a modal tune, you can chose how to interpret the chords. A modal tune would be only one or very few different chord qualities. I.E. "Impressions": has only minor chords (Dm7 and Ebm7). The composer (John Coltrane) decided to choose the dorian scale. He could have chosen phrygian, aeolian, or other scales that spell a minor chord too. He decided for that mood probably because dorian is the most use scale for minor chords in jazz. I would say it is the brightest of the minor scales, due to its major 6th.

Hope this makes things a little clearer for you. Ask, if you need more information.

Sandra

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