First; a question: What notes are in a Gsus4 chord?
OK. Modes.
The major and minor keys are probably about 99% of modern western music but they are just two of seven different modes possible with the note distibution (two half steps scattered amongst all the whole steps) available to western music. They are often described in relation to the white notes on a piano. The standards are the major (C to C on a piano) and minor (A to A on a piano, but there are variations called harmonic and melodic minor that would just confuse things so we'll stick to what we can call the pure minor, A to A). These are not the only possibilities and, in fact, in the days of Gregorian chant, were not used very much, if at all. The modes have been given Greek names (that have nothing to do with anything the ancient Greeks called any corresponding modes but). These modes can be roughly divided into major and minor modes based on whether they had a major or minor third.
Starting with the one we call Ionian they are:
Ionian - This is the major mode. C to C on the piano.
Dorian - D to D. A minor mode. D minor has one flat, Bb. This is the sixth. It is a B natural in Dorian, so Dorian is minor with a raised sixth.
Phrygian - E to E. A minor mode. E minor has one sharp, F#. The F is natural in Phrygian, so Phrygian is minor with a minor second.
Lydian - F to F. A major mode. F major has one flat, Bb. The B is natural in Lydian, so Lydian is major with an augmented fourth.
Mixolydian - G to G. A major mode. G major has one sharp, F#. The F is natural in Mixolydian, so Mixolydian is major with a flatted seventh.
Aeolian - A to A. This is the pure minor.
Locrian - B to B. This is where things get scary. It's a minor mode but. B minor has two sharps, F# and C#. They are both natural in Locrian so Locrian is minor with a flatted second (the C#) and a diminished fifth (the F#). Since the perfect fifth is so basic to Western music use of the Locrian is almost unheard of and, indeed, thought by some to be Evil.
Anyone still awake can go back to sleep now, and pleasant dreams (as if)
