Modes, and the chord that holds each one up
The seven rotations of the major scale, each with its own centre and colour, defined by the degree that changes against major or minor; a mode is heard through the chord that holds it, not through the scale it came from.
The white keys of the piano, C to C, are the major scale. The same white keys, D to D, are another scale, with the semitones in different places and a different character. E to E, another. They are seven starting points over the same seven notes, and each one is a mode. The name comes from Greece by way of the medieval Church; the use comes from jazz, from Brazilian popular music and from rock.
The seven rotations
Each mode is the major scale started from a different degree. The names, in order of the degrees:
- Ionian — from the first degree: it is the major scale.
- Dorian — from the second.
- Phrygian — from the third.
- Lydian — from the fourth.
- Mixolydian — from the fifth.
- Aeolian — from the sixth: it is the natural minor scale.
- Locrian — from the seventh.
D Dorian and E Phrygian use the notes of C major; what changes is the centre, and with the centre changes where the two semitones fall in relation to it. That is what gives each mode its colour.
Each mode is one altered degree
The way to recognise a mode is not to remember which degree of the major scale it came from: it is to compare it with the major or minor scale starting on the same note, and see which degree changed. Three modes are major, with a major third; three are minor; one is neither.
The major ones, against the major scale on the same tonic:
- Lydian — major with a raised fourth. F Lydian has a B natural, not a B flat.
- Mixolydian — major with a lowered seventh. G Mixolydian has an F natural, not an F sharp.
The minor ones, against the natural minor on the same tonic:
- Dorian — minor with a raised sixth. D Dorian has a B natural, not a B flat.
- Phrygian — minor with a lowered second. E Phrygian has an F natural, not an F sharp.
And Locrian, minor with a lowered second and fifth, which has no perfect fifth and is therefore hardly ever used as a centre: there is no stable chord to hold it up.
The mode is heard through the chord
D Dorian sounds Dorian over a D minor chord. Over C major, the same notes sound like C major, because the ear takes the chord as the centre and hears the scale from there. A mode is not a scale played anywhere; it is a scale played over the chord that holds it, and it is the chord that makes it sound modal.
Over D minor seventh, the B natural — the raised sixth degree — is the Dorian note; swap it for a B flat and the same chord turns Aeolian. The difference in colour is one note, and the note only has a name because a chord underneath is saying which is the tonic.
The first is D Dorian; the second, D Aeolian. Sing both over a D minor and hear the sixth degree decide.
Where the modes turn up
Mixolydian is the scale of the dominant chord and of nearly all rock and blues with a major chord and a minor seventh: G Mixolydian over G7. Dorian is the minor of modal jazz and of a good part of Brazilian popular music, the minor with the bright sixth. Lydian is the major with a fourth that does not weigh, the sound of an open film score. Phrygian is the minor with a darkened second, the Spanish sound and the sound of tension.
G7 and F major, and the scale that fits both is G Mixolydian: G major with an F natural. It is the most Mixolydian progression there is, and it is in thousands of songs.
What to take from here
The modes are the major scale started from each of its degrees, and each is defined by the degree that changes against the major or natural minor on the same tonic: Lydian and Mixolydian are major with one altered degree, Dorian and Phrygian are minor with one altered degree, and Locrian has no perfect fifth. A mode sounds modal over the chord that holds it, and it is by that chord, not by the scale it came from, that you think while playing it.