Why can’t you use the same backing track for all modes of a scale?

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.