I am seeing lots of statements online to guitarists that they should be careful to use the specific backing track for a mode. It seems to me that you should be able to use one backing track for all modes of a given scale as long as it's compatible with the parent scale for those modes (by 'parent scale' I mean the Ionidan mode... I understand they are all relative and as such none is really the 'parent'). This is because in my (likely incorrect) understanding that the problem of using the wrong scale would be clashing notes, but since the parent scale has all the same notes as its modes (right?) anything played in those modes would not clash with a backing track compatible with the parent scale. What am I not getting?
Modes are defined by two things:
- (1) the home note, i.e. the tonic, and
- (2) the relative harmony around the tonic.
A backing track has much more power in setting the home note than any guitar solo. You can play the D Dorian scale all you like, but if the bass player keeps playing the C note, you lose the battle, the total mode (which is a feeling really) is most likely going to be C Ionian. However, if the bassist plays only the C note, and your solo is the only element creating harmony around the C, then you can create the feeling of any C-based mode such as C Dorian, C Lydian or C Mixolydian.
Here's an example of a well-known modal melody in F Lydian, with two different "backing tracks". First an F major backing track, which together with the melody keeps the whole thing nicely in Lydian.
But if we change the "backing track" to C major, what happens? It's not really Lydian any more.
Any backing track will basically use chords/harmonies from a particuar key/mode In that track, one chord in particular will feel like 'home'. That will be the key chord - literally.
Let's take C major as the Ionian - parent - key. A backing track that uses chords from that key will home in on C major. There will be no confusion as to where it belongs. You could use all the notes from, say, D Dorian, or G Mixolydian to play over it, but you'd find yourself pinpointing C more than any other.
Were the track in D Dorian, you wouldn't be happy targetting C, because D would be 'home'. Finishing on a C just wouldn't sound satisfying.
I hope this makes sense. You might need to try it all out to understand.