So I've just made the commitment to learning modes after putting them off as something that is unattainable; and just wanted to make sure I understand; so far.

(Key of C)

I understand that Ionian and Aeolian are the major and minor scale, respectively. But if a song I'm listening to has the progression Dmaj - Gmaj - Dmaj - Cmaj - Dmaj (just throwing that out there); is that D Dorian?
no....dorian is the notes of the cmaj scale played from d-d


d major is d,e,f#,g,a,b,c#,d

the diference is it has a b3, and a b7

so 1,2,b3,4,5,6,b7

which in ts form is TSTTTST......which is all.....IRELEVANT

to UNDERSTAND modes you need to UNDERSTAND one thing....that they are inversions (starting on different degrees) of the major scale...no new fingerings to learn...if you can solo all over the neck in c maj.....do it...but start and end on d...wow....d dorian

i think like this

ionian c,d,e,f,g,a,b,c 1,2,3,4,5,6,7, major scale
dorian d,e,f,g,a,b,c,d 1,2,b3,4,5,6,b7 minor w maj 6
phrygian e,f,g,a,b,c,d,e 1,b2,b3,4,5,b6,b7 minor w b2
lydian f,g,a,b,c,d,e,f 1,2,3,#4,5,6,7, maj w #4
mixolydian g,a,b,c,d,e,f,g 1,2,3,4,5,6,b7 maj w b7
aolian a,b,c,d,e,f,g,a 1,2,b3,4,5,b6,b7 minor
locrian b,c,d,e,f,g,a,b 1,b2,b3,4,b5,b6,b7 minor w b2, b5

learn the bit on the right..... get your head round this idea it looks so complicated...but look at the letters, there are only a,b,c,d,e,f,g there..... modes are there PURLEY for the fact that

when playing over a c maj chord....c is home, e, and g sit nicely too...

when playing over a d min chord....c is no longer home...but why were in the key of c....
c is the b7 of d...its not a point of rest....rest is d, or g or a

the key (or fingerprint as i explain to my students) hasnt changed at all..... once you have all this comitted to memory...then you can start experimenting

for example why play the major scale over a c maj chord....the only notes are C,E,G...or 1,3,5.... that could be lydian...or mixolydian

so anyway.... a dorian progession would be dmin, f/d, g/d

just tune your e down to d an play dmin, f (with the low open d) an g (with the low open d)

youll hear the quality of the mode like this