Harmonic Function

A chord name tells you which notes the chord contains. Harmonic function tells you what that chord is doing at a particular moment.

C major contains C-E-G. In the key of C major it is I, the tonic chord. In the key of F major the same C-E-G chord is V, the dominant. Its notes have not changed; the tonal center around it has.

Function therefore belongs to a chord in context. The key, the chords before and after it, the bass and the melody all help establish that context.

Play C major by itself: C-E-G does not announce one key. Now place it in two progressions.

In C major, play C-F-G-C. The first and final C chords are tonic. They frame the phrase and establish C as home.

In F major, play F-B flat-C-F. C major now occupies the dominant position. Its E is the leading tone to F, so the chord creates tension instead of rest.

This is why function is more useful than assigning a permanent feeling to a chord shape. C major can close one phrase and leave another waiting for resolution.

In G7-C, the notes B and F create the clearest internal motion. B rises by semitone to C. F falls by semitone to E. These two small movements turn the tritone B-F into the third C-E.

The bass usually moves from G to C, a descending fifth or ascending fourth. That root motion reinforces the arrival.

Listeners also learn tonal expectations through repeated exposure. Western tonal music uses dominant-to-tonic motion so often that the arrival becomes predictable. Voice leading supplies the motion; musical experience strengthens the expectation.

Chords in the same functional area can often substitute for one another while preserving the broad direction of a phrase.

Compare C-F-G-C with C-Dm-G-C. F and Dm share F and A. The second progression changes color while keeping the same tonic-predominant-dominant-tonic route.

The categories are useful tendencies. iii can connect tonic and predominant areas, and vi can also begin a deceptive continuation after V. The surrounding progression decides which role is most convincing.

The same three-part model works in minor, but the dominant often requires an altered note.

A natural minor has G natural. Its diatonic v chord is Em: E-G-B. That chord has no leading tone a semitone below A, so its return to Am is relatively soft.

Raise G to G sharp and the chord becomes E major or E7. G sharp leads to A, and E7 contains the tritone G sharp-D. This is the main reason harmonic minor raises scale degree 7.

Compare Am-Dm-Em-Am with Am-Dm-E-Am. The first can sound modal and less directed. The second creates a stronger dominant-to-tonic arrival.

Functional harmony explains music organized around a tonic and directed dominant resolution. It works especially well for common-practice classical harmony, hymns, standards and many tonal pop progressions.

Modal harmony may hold one center through drones, characteristic scale degrees and repeated chord colors. Blues can use dominant-seventh sonorities on I, IV and V without making all three chords classical dominants. A four-chord pop loop may create continuity through repetition and arrangement instead of a final cadence.

Use function when it predicts the motion you hear. When it does not, examine the bass, melody, mode, groove and form before forcing the chords into tonic, predominant and dominant categories.