I'm looking for some useful historical references for modal study. Specifically, great books or texts on how modes evolved, progressed and became the elusive subject they are today.
What resources have been useful to you to have it finally click? I would imagine there are some basic texts in the formal music school context so I'm looking for anything like that, but useful videos that made the difference for you are also good.
I'm feeling pretty solid on my diatonic tonal study and want to branch out into modal studies with a solid foundation of how they evolved.