Can someone tell me why modes are useful/important? This is probably the next music theory subject I want to learn about.
hmmm, i know them, but explain them? shit.
basically they are different scales that all are derived from the basic Major scale, by making your root note a different not of the scale.
when you make chords from the major scale by using the 1 3 5, 2 4 6, etc. you get these:
Maj, Min, Min, Maj, Maj, Min, Dim
and for more detail, you use the sevenths as well (1 3 5 7, 2 4 6 1, ...)(the modes are in () here)
Maj7 (Ionian (Major)), Min7 (Dorian), Min7 (Phrygian), Maj7 (Lydian), Dom7 (Mixolydian), Min7 (Aeolian (Minor)), Half Dim7 (Locrian)
basically when you get these basic chords, the modes are scales that fit within the chord, and within the overall tonality of the song.
If I have a G Dom7th chord, I would most like be using the Mixolydian mode, because it is derived from the scale degree.
If I had a progression of Dmajor to Emajor, that would tell me the we are using the 4th and 5th degrees of the major scale to get those, though our parent scale may not be obvious just from using those two chords.
this was probably a horrible and half assed way of trying to explain them, though it is extremely important to learn and know them as best you can for playing and improvisation.