Harmonic functions
Tonic, predominant and dominant, the three roles the chords of a key play, and the reason a progression feels like it's "going somewhere".
Applied
Content under musical review. It may contain inaccuracies.
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Tonic, predominant and dominant, the three roles the chords of a key play, and the reason a progression feels like it's "going somewhere".
Applied
In a key, every chord has a role. Some feel like rest, some get things moving, and some create the tension that pulls you back home. These roles fall into three functions: tonic (T), predominant (PD, also called subdominant) and dominant (D). Understanding them lets you read any progression as a small story: stability, departure, tension and return.
The full cycle in C major, one chord after another:
Stop after the third chord: the phrase is left hanging.
| Function | Degrees in major | In C major | Feeling |
|---|---|---|---|
| Tonic (T) | I, vi, (iii) | C, Am, Em | rest, home |
| Predominant (PD) | ii, IV | Dm, F | moving away, preparing |
| Dominant (D) | V, vii° | G, Bdim | tension, wants to resolve |
Chords with the same function share notes. Dm and F have F and A in common; G7 and Bdim both contain the tritone B–F, the source of dominant tension.
String 6, Fret 1: F2 · ♭7 · Seventh
Open the key in the harmony lab: each chord is shown with its degree and function. Then hear two versions of the same T → PD → D → T journey, swapping the chords in each function:
Functions in C major I – IV – V7 – I vi – ii – V7 – IBoth tell the same story in a different colour.
The typical progression follows T → PD → D → T. Moving the other way (D → PD) is possible, but it sounds weaker or more "modern", something common in rock and pop.
When you analyse a song, write the roman numerals first and then the functions. Patterns that looked different turn out to be the same scheme with other chords.
In A minor the functions are the same, but the chords change: tonic on i (Am) and VI (F); predominant on iv (Dm) and iiø (Bm7♭5); dominant on V (E or E7, with harmonic minor's G♯) and vii°7 (G♯dim7). Without that G♯, the fifth degree is Em and the dominant loses its pull.
Functions in A minoriii is the most ambiguous chord: it shares two notes with I and two with V, so it can extend the tonic or lead toward the dominant depending on context. Kostka and Payne place it in the chain of descending fifths (iii → vi → ii → V → I), and Piston gives a table of "usual root progressions" by degree that shows the same order.
vi also plays a double role: as a tonic substitute in the deceptive cadence (V → vi) and as the chord that starts the path toward the predominant. Function doesn't live in an isolated chord, but in what it does within the phrase.