Originally Posted by Pacman -----Learning the modes in a parallel method (C Ionian, C dorian, C, phrygian, etc) is by far a better way to get a handle on modes. You'll learn the construction and understand the differences between them. Go that way, and don't look back.
There are two ways of looking at modes. Relative modes where the key changes and the notes stay the same and then Parallel modes where the key stays the same and the notes change. Both get to the same sound, but, go down two different roads getting to that sound. Internet answers to your questions are normally correct, however, the person answering the question may be speaking in Relative or Parallel and most do not tell you which one. So you get confused.
Relative is easier to teach and perhaps easier to understand. Relative is where you are taught that the C scale C, D, E, F, G, A, B, C and is the same as the Ionian mode and then the C scale starting on D - D-E-F-G-A-B-C-D is the Dorian mode, etc
Parallel modes keep the same key and the notes change. C Ionian would be C, D, E, F, G, A, B, C. I think in scale degrees and major scale patterns so to me the C Parallel mode would be R-2-3-4-5-6-7-8. For example:
Ionian = R-2-3-4-5-6-7-8 - Major mode and home base for all major modes.
Lydian = R-2-3-#4-5-6-7-8 - Major mode one note different.
Mixolydian = R-2-3-4-5-6-b7-8 - major mode one note different.
Aeolian = R-2-b3-4-5-b6-b7-8 - Minor mode and home base for all minor modes.
Dorian = R-2-b3-4-5-6-b7-8 - Minor mode and one note different.
Phrygian = R-b2-b3-4-5-b6-b7-8 - Minor mode and one note different.
Locrian = R-b2-b3-4-b5-b6-b7-8 - Minor and Diminished and Locrian has two notes different.
Different than what? Different from the major or minor home bass. Home base for major modes is the Major scale and home base for minor modes is Natural Minor scale.
Now the confusing part. We may think of C Dorian in Parallel modes as being R-2-b3-4-5-6-b7-8 or D-E-F-G-A-B-C-D in Relative modes. The D major scale is D-E-F#-G-A-B-C#-D not D-E-F-G-A-B-C-D, but, drum roll ---- So C Dorian flats the 3rd and 7th degrees. Same thing.
You are taught Relative modes because they are easy to teach. I, like Pacman, find parallel much easier to use in a molidic situation.
If I want the Dorian sound (attractive minor sound) I use the natural minor scale and sharp the b6 back to a natural 6. If I want the Lydian sound I use the major scale and sharp the 4 to get the Lydian sound. Mixolydian flat the 7. Phrygian - OK it's minor so I revert to the natural minor scale and flat the 2.
Scott Devine's video on Modes explains this very well.
Why use a mode? For it's sound. Now the next thing you must take into account. If you want the modal sound to sustain you need to be playing this mode over a modal vamp not a normal V-I chord progression. Why? A V-I chord progression always calls your attention to the V-I tonal center. All your modal melody will be drowned out with the return to the tonal center of the chord progression, namely the I tonic chord's sound. When using modes use a modal vamp. Notice Scott Devine's video uses the droning E string as his modal vamp to play his modes over. Got to have the modal signature note droning in the background for the modal sound to sustain. Modal signature note??? The note that is different from the parent major or minor scale. Another long story best started here
http://www.riddleworks.com/modalharm3.html.
Good luck.