[Harmonics] Course 7 3 Functions of Major Diatonic Chords

3 Functions of Major Diatonic Chords 

7 chords that are created on the major scales have different characteristics. However, there are three chords that have the most influential characteristics. They are IM7 (tonic), IVM7 (subdominant) and V7 (dominant). I will explain them based on the diatonic chords that are created on the C major scale. 

Tonic 

Diatonic chords on the C major scale are CM7, Dm7, Em7, FM7, G7, Am7 and Bm7b5. The first CM7 is a tonic chord among them and it shows a stable sound as it has a root C which is a root of the C major scale. Most of the tunes end with this tonic chord offering a sense of completion. 

Dominant 

The fifth G7 in the diatonic chords of the C major scale has an unstable sound and has a strong tendency to move to a tonic one. 

Dominant Motion 

Musical motion can be created by repetition of stable and unstable sounds. Chord progressions which try to move from dominant chords that are not stable to the stable chords are called ‘dominant motion’. 

The reason that such dominant motion is powerful is the interval of the chord tones that G7 as a dominant chord has. It’s because the chord has the third B and the seventh F which result in the augmented fourth that are not stable. Such augmented fourth is called tritone. 

Such tritone by B and F leads to a powerful motion in which it tries to resolve its instability by half tone lowering the notes B and F to C and E of the tonic chord (CM7). 

One more thing is that the motion of the circle of fifths that we have learned from the previous course and the motion of the root up by the perfect fourth or down by the perfect fifth can be considered to be the most powerful. 

Subdominant 

The fourth FM7 in the diatonic chords of the C major scale is a subdominant chord. It is not powerful as the tonic or dominant chords. However, it also has a tendency to gradually move to the tonic chord. The chord progression typically found in so-called ‘Amen’ part of church music shows this kind of chord progressions. 

Substitute Chord 

The remaining Dm7 (iim7), Em7 (iiim7), Am7 (vim7) and Bm7b5 (viim7b5) of the C major scale are classified as substitute chords which replace either one of the tonic, subdominant and dominant chords. Criteria for such classification are based on the chords that share three notes in common among four notes of the seventh chords. 

Substitute chords for the tonic chord 

Substitute chords for CM7 (IM7) are Em7 (iiim7) and Am7 (vim7) and let’s look into what notes they share together with the following figure. 

Substitute chord for the dominant chord 

A substitute chord for G7 (V7) is Bm7b5 (viim7b5). These two chords also share three notes in common. 

Substitute chord for the subdominant chord 

A substitute chord for FM7 (IVM7) is Dm7 (iim7). These two chords also share three notes in common. 

Full Cadence 

Full cadence refers to a chord progression that uses the major chord progressions of the subdominant, dominant and tonic chords. 

Two - Five 

Two - Five refers to a chord progression that uses iim7 which is a substitute chord for the subdominant chord and a chord progression of iim7 to V7 is called Two - Five and it is one of the most popular chord progressions in modern music. So please keep it in mind.