Look at a piano, it has white keys that repeat the same 7 notes so it goes
C-D-E-F-G-A-B-C-D-E-F-G-A-B-C-D-E-F-G-A-B-C-D-E-F-G-A-B-C-D-E-F-G-A-B-C etc and so on it goes.
So take any 8 notes in a row form this and you have a mode not a scale. Confusion is some of the modes are used as scales like the C scale...C-D-E-F-G-A-B-C You will find notes that relate to scales.
But as the notes are so in order, so are the intervals in between them.
So the same notes listed above have these intervals between them (T-tone, S-Semitone)
T-T-S-T-T-T-S-T-T-S-T-T-T-S-T-T-S-T-T-T-S-T-T-S-T-T-T-S-T-T-S-T-T-T-S
etc. Now this represents the white keys again but this time with intervals, but in between tones, shown above as the sharps, are the black keys on the piano, the sharps and flats if you will of music depending on the scales.
So it would look like this, and notice the groupings of twos and threes the black note take inbetween the Tones, exactly the same as a piano
..C#.D#....F#G#A#.....C#.D#....F#G#A#....
C...D...E.F...G...A...B.C...D...E.F...G...A...B.C
Now we can see the relationship to the notes and the intervals as the appear on a piano. On the bass all frets are semi tones apart, so therefore all notes on any one string are a semitone apart next to each other. Because of no black notes above as on a piano, a bass as all its semitones side by side and reads. E-F and B-C are semitones because of the order of intervals that depict it as Ionian, and therefore cannot have a note between them in Westen music.
C-C#-D-D#-E-F-F#-G-G#-A-A#-B-C etc
All modes are.. are inversion of a C scale by intervals, and so the need for sharps and flats when using notes to keep the intervals correct.
So if we take starting note and play 8 notes in a row all white we have the modes. If you understand theory, modes are just inversions on a C scale
Ionian = Root C-C 8 white notes on the piano the C major scale
Dorian is D-D 8 white notes on the piano, 1st inversion
Phrygian is 8 white notes on the piano, 2nd inversion
Lydian is F-F 8 white notes on the piano, 3rd inversion
Mixolydian is G-G 8 white notes on the piano, 4th inversion
Aeolian is A-A 8 white notes on the piano (tonic minor scale), 5th inversion
Locrian is B-B 8 white notes on the piano, 6th inversion.
Modes are just what you have learned in different positions, thats why they want to be one of the last things anyone learns IMO. When introduced to early without proper education or understanding they are a distraction, a cul-de-sac, a waste of time, pointless, etc you name it. There are better things to get in place first, foundation knowledge to support modes when the time comes to study them, and for me that study would be brief as they can be seen as pointless, limiting and restrictive in most musical situations IMO.
