Diatonic Chords

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Chord progressions in tonal music are not random sequences. There are certain patterns and relationships between chords that are typical and reinforce the key center of a piece. As with the chords themselves, the progressions tend to be based on the major or minor scale.

Using the key of C major as an example, consider a series of triads built diatonically on each degree of the scale:

[EXAMPLE]

The chords built on the first, fourth, and fifth degrees are major triads. These chords are indicated using capital roman numerals: I, IV, and V. The second, third, and sixth degrees are minor triads, and are indicated with lower case roman numerals: ii, iii, and vi. The seventh degree is a diminished triad, which is also indicated by a lower case roman numeral, usually with a small circle or degree sign, as in viio, to distinguish it from the minor triads.

These same relationships of degrees to chord qualities hold in any other key. For instance, here are the triads in the key of E:

[EXAMPLE]

If the triads are extended to seventh chords, we find that the minor triads become minor seventh chords, the diminished triad becomes a half-diminished seventh, two of the major chords become major seventh chords, and the major chord on the V becomes a dominant seventh:

[EXAMPLE]

In minor keys, the chord qualities of the triads built on the various scale degrees differ from those found in major keys. In the natural minor, the chords are:

[EXAMPLE]

As was observed earlier, the harmonic minor raises the seventh degree in order to make the minor v chord into a major chord. The raised seventh degree can be used in the other chords as well, yielding:

[EXAMPLE]

Note the notation for the augmented III+ chord.

The melodic minor generates the following harmony:

[EXAMPLE]

Recognizing chords that are diatonic to a key can be useful in improvisation, because it suggests that melodies based on the scale of the key will work over the chord. The relationship between harmony and melody is discussed at length in subsequent chapters.

Copyright 2000 Outside Shore Music
Authored by Marc Sabatella

Diatonic Chords