HARMONIC FUNCTION Tonal music is hierarchical: some notes and chords are more stable than others.

The interplay of tension and stability is what gives music its sense of motion and progression through time.

The sense of tension and release is created largely through the interplay of consonance and dissonance.

There are two kinds of consonance and dissonance, acoustic and contextual.

Acoustic consonance and dissonance occurs between two or more notes, according to their relative frequencies. In music theory, we measure this difference using intervals.

CONSONANCE DISSONANCE

P8 P5 sometimes P4 3rds & 6ths sometimes P4 2nds & 7ths tritones

In the same way, chords are acoustically consonant or dissonant, depending on the intervals they contain.

CONSONANCE DISSONANCE

maj & min added 6th min & maj half-dim aug & dim dom & dim alt & 9th triads chords 7th chords 7th chords triads 7th chords chords

Contextual consonance and dissonance involves one or more notes, according to their stability within a key. Normally, 1, 3, and 5 (the notes of the tonic triad) are stable, 2, 4, 6, and 7 (the other diatonic notes) are unstable, and nondiatonic notes ( 2 and 4/ 5) and enharmonic notes (2, 6, etc.) are even less stable.

The tonic triad as a unit is also stable, and so are III (especially in minor) and VI, the chords a third away from the tonic in either direction, which share two notes with the tonic triad and thus behave similarly. *Note: this is true more generally—because our system of harmony consists of chords made of stacked thirds, chords whose roots are a third apart share most of their notes, and typically behave the same way. Subdominant-function chords such as II and IV are less stable, and dominants such as V and VII still less so. Thus, within the context of a key, I is usually stable and V is usually unstable, even if they are both major triads.

Tonic chords are in the upper half of the circle: I, VI, and sometimes III. Subdominant chords are in the left half: II, IV and VI. Dominant chords are in the right half: V, VII, and sometimes III. All the chords are shown as major to simplify the diagram, but this applies to other chord qualities too. For example, subdominant chords include

ii, ii°, IV, iv, vi, and ()VI.

Harmonic function is correlated with the consonance or dissonance of a chord:

tonic chords are the most stable; they serve as points of rest

subdominant (also called pre-dominant) chords are less stable; they usually lead to dominant chords

dominant chords are the least stable; they create tension and usually resolve to tonic chords

Harmonic function is determined by two factors: chord identity and chord behavior. Chord identity, in turn, is determined by two factors:

chord quality (= acoustic consonance/dissonance)

scale degree of chord root (= contextual consonance/dissonance) Chord quality and harmonic function

triad qualities:

major or minor triads are acoustically consonant, and can have any function

diminished and augmented triads are acoustically dissonant, and usually function as dominants

seventh chord qualities:

major and minor 7th chords and added-6th chords are mildly dissonant they can function as tonics, but are most often subdominants

half-diminished 7th chords are somewhat more dissonant and usually function as subdominants

dominant and diminished 7th chords are still more dissonant and usually function as dominants Scale degree and harmonic function

Chords built on 1 are usually tonics.

Chords built on 2 are usually subdominants (this includes II).

Chords built on 3 are either tonics (III in minor) or dominants (iii or III in major, IIIaug in minor)

Chords built on 4 are subdominants (IV and iv).

Chords built on 5 are dominants.

Chords built on 6 are either tonics (as in a deceptive cadence) or subdominants.

Chords built on 7 are usually dominants (this includes VII). Note that chord quality and scale degree usually correlate with the same harmonic function:

for example, the most common seventh chords built on 2 are minor 7th chords (in major) and half-diminished 7th chords (in minor), which have subdominant function

the most common seventh chord built on 5 is a dominant 7th, which has dominant function

Chord behavior

The most important determinant of harmonic function is what the chord actually does.

For example, if it moves to a dominant, it is most likely a subdominant (or pre-dominant).

If it is between two dominant chords, it is most likely an expansion of the dominant.