Harmonic Function

Harmonic function is the job a chord does in a key. Tonal music gives its chords three basic roles:

• Tonic (T): stability, home. Chiefly I, and sometimes vi or iii.
• Predominant (PD), also called subdominant (S): movement away from home that prepares the dominant. IV and ii, with their seventh chords and inversions.
• Dominant (D): tension that wants to resolve to the tonic. V, V7, vii° and vii°7.

The basic cycle

A typical phrase moves T → PD → D → T: it starts at home, leaves, builds tension and resolves. I – IV – V7 – I is the plainest version. Chords that share a function can stand in for one another, so vi – ii6 – vii°6 – I follows the same path with different chords:

▶Primary chords0:15▶Substitutes0:14

Why chords share a function

Chords with the same function share notes. ii (D–F–A) and IV (F–A–C) have F and A in common, and both contain the fourth scale degree, F, which leans toward the dominant. vii° (B–D–F) is V7 (G–B–D–F) without its root, so it carries the same two tendency tones, B and F. vi (A–C–E) shares C and E with I (C–E–G), which is why it can replace I in a deceptive cadence.

Using function

• Analysis: label a progression T, PD and D to see the shape of a phrase at a glance.
• Harmonizing: when IV sounds too plain, try ii; when a cadence should surprise, replace I with vi.
• Composing and improvising: knowing a chord's job lets you change the chord without changing the direction. In jazz the ii–V–I progression is PD – D – T, and a tritone substitution swaps one dominant chord for another.

Where the idea comes from

The term "function" for these roles is usually credited to the German theorist Hugo Riemann, writing in the late 19th century. Textbooks still differ on the details: some call the middle group "subdominant", others "predominant", and they disagree about where iii and vi belong.

Practice with Tonic & dominant harmonies, The primary chords: I, IV & V and Harmonize a melody 2.