Musical modes

Modal theory is simple to understand, still this simple concept has caused mode confusion that any other musical principle in music. For most musicians the term scale and mode are interchangeable. There is some truth to this perception, understanding the difference is crucial.

A scale is defined as a series of notes, arranged by order of pitch between the root and a octave. Any number of notes between the root and the octave can be considered a scale. Still there are only a few that have gained acceptance in western music.

A mode can be though of as a way of manipulating the notes of a scale in order to generate a greater variety of sounds. It's a way of opening up the sound and enter into a realm of exotic sounds. In this article the focus will be on the modes of the major scale.

C major scale consist of C, D, E, F, G, A, B, C with the intervals R, 2, 3, 4, 5, 6, 7, 8. Any combination of notes played from the scale will yield a different interval structure. The interval structure is what gives the scale it's sound quality and mood.

When playing the scale back and forth you can hear a distinct sound quality of the scale. The relationship of the intervals in the scale always stays the same and so does the sound. A crucial point is the root note and the octave since they are always the starting and end points. If you change the root note to D but still play the same scale notes you will hear the same scale staring from a different pitch. This is where modes come into play.

Modes allow you to generate an interval structure that is different from the major scale and produces a unique sound quality. Modes are derived by playing a scale by starting and stopping on a note within the scale other that the root note. With the C major scale as an example (C, D, E, F, G, A, B, C) start and stop on a D note instead of the C and you get:

D, E, F, G, A, B, C, D

You are still playing the notes of the C major scale but starting and stopping on D thus changing the root note from C to D. You may have to play the scale several times  before you begin to hear the D tonal center. A helpful tool to nail the tonal center is to have a D note sound over the scale or the D minor chord the II chord of C major or the I chord of D Dorian.

By comparing the modal scale to it's major counterpart you can see that the D major scale is:

D, E, F#, G, A, B, C#, D

Your new modal scale contains a F and C instead of the sharp counterparts in the D major scale. Altering the 3rd and the 7th changes the scale and sound quality dramatically. This new scale is called D Dorian mode. D is the root note, Dorian is the classification of the new sound and mode means that you start and stop on a note other that the root of the parent scale. The new scale is a D scale, not a C scale. It is not a D Dorian substitute for C major, it is D Dorian.

Modes arrangements

The modes can be arranged in the following sequence, where each mode has one more shortened interval in its scale than the one preceding it.

mode	white note	Intervals in the modal scales
		prime	second	third	fourth	fifth	sixth	seventh	octave
Lydian IV	F	perfect	major	major	augmented	perfect	major	major	perfect
Ionian I	C				perfect
Mixolydian V	G							minor
Dorian II	D			minor
Aeolian VI	A						minor
Phrygian III	E		minor
Locrian VII	B					diminished

The first three modes are termed major, the remaining four minor, governed by their third scale degree.

The Locrian mode is traditionally considered theoretical rather than practical because the interval between the first and fifth scale degrees is diminished rather than perfect, which creates difficulties in voice leading. However, Locrian is recognized in jazz theory as the preferred mode to play over a ii half-dim7 chord in a minor ii half-dim7-V7-i progression, where it is called a 'half-diminished' scale.

Major modes The Ionian mode is identical to a major scale. The Lydian mode is a major scale with a raised fourth scale degree. The Mixolydian mode is a major scale with a lowered seventh scale degree.

Minor modes The Aeolian mode is identical to a natural minor scale. The Dorian mode is a natural minor scale with a raised sixth scale degree. The Phrygian mode is a natural minor mode with a lowered second scale degree.

Diminished modes Locrian is the only mode whose fifth is not perfect. This interval is enharmonically equivalent to the augmented fourth of the Lydian mode. The Locrian's (I)'s seventh chord is naturally a half diminished seventh which is a diminished triad with a minor seventh on top.

Chords

In jazz, the modes correspond to and are played over particular chords. (This is not entirely true. For this usage, scale on a chord, the correct term is "chord scale", not mode. Ex: The dorian chord scale is commonly played over the II-7 chord in a major key. Being in the dorian mode signifies that that particular chord is the tonic chord.) The chord examples below are shown for the modes of the key of C. For example, over an Fmaj7b11 chord, musicians typically play notes from the F Lydian mode (a Lydian chord scale over a IVma7 chord).

Mode	Ionian	Dorian	Phrygian	Lydian	Mixolydian	Aeolian	Locrian
Chord	Cmaj7	Dm7	Esusb9 (or Em7)	Fmaj7b11	G7	Am7	B half-dim (Bm7b5)

Although both Dorian and Aeolian can be played over a minor seventh (m7) chord, the Dorian mode is most commonly used in straightahead jazz because the Dorian mode has a whole step between the 5th and 6th scale degrees, in contrast to the more jarring half step in the Aeolian. Also note that the most common jazz cadence or chord progression is a ii-V-I which suggests Dorian mode in the case of the ii chord.

Similarly, over a half-diminished (half-dim or m7b5) chord, many jazz musicians will alter the Locrian mode by raising the second degree of the scale by a semitone, in order to form a major ninth over the chord (e.g. Cb over B half-dim), rather than the more dissonant minor ninth (e.g. C natural over B half-dim). This scale is also called the 6th mode of the melodic minor. And over the "susb9" chord, the sixth scale degree of the Phrygian mode is often raised by a semitone, in order to make a major sixth in the chord, rather than the more dissonant minor sixth. This mode is also called the 2nd mode of melodic minor. See Other modes below for more about the melodic minor modes and their associated chords.