What chords do: numerals and functions
A chord’s name says what it is: G7 is G, B, D and F. Its numeral says what it does in the key: in C major, G7 is V7, the chord on the fifth note, the one that pulls the music home. This chapter is about that second kind of name, and about how chords pull on each other.
Roman numerals
Number the notes of the scale from 1 to 7, and name each chord by the note it is built on, in Roman numerals: uppercase for a major chord, lowercase for a minor one, with ° for diminished and + for augmented. In C major:
| I | ii | iii | IV | V | vi | vii° |
|---|---|---|---|---|---|---|
| C | Dm | Em | F | G | Am | Bdim |
With sevenths, the numeral takes the chord’s figure: Imaj7, ii7, iii7, IVmaj7, V7, vi7, viiø7.
The point of numerals is that they don’t depend on the key. ii, V,
I is Dm, G, C in C major, Em, A, D in D major and Gm, C, F in F
major, and it does the same thing in all of them. Learn a progression
by its numerals and you know it in every key. On the chord sheet you can
even type numerals: ii7 V7 Imaj7 in B♭ major is written Cm7, F7,
B♭maj7 (see The chord sheet).
Home, away and tension
The seven chords of a key do three jobs, which harmony books call functions. Ferrous Lineup shows them on the harmony keys, in a word and a colour:
| Function | Colour | Chords | What it does |
|---|---|---|---|
| Tonic | blue | I, and iii and vi | home: the music rests here |
| Subdominant | green | IV and ii | moves away from home |
| Dominant | orange | V and vii° | tension that pulls back home |
Why these groups? Chords that share notes do similar jobs. vi (A C E) shares two of its three notes with I (C E G), and so does iii (E G B); that is why a song can end a phrase on vi and still sound nearly at home. ii (D F A) shares two notes with IV (F A C). And vii° (B D F) is V7 (G B D F) without its root.
The dominant pulls because of two notes. Its third, B in G, is the leading tone, a semitone below home, and it wants to rise to C. In G7, the seventh F wants to fall a semitone to E. B and F are a tritone apart, the most restless interval there is, and moving inward to C and E settles it. That pull is the engine of most music in major and minor keys.
Cadences
A phrase of music ends on a cadence, the way a sentence ends on a full stop or a question mark:
| Cadence | Chords | Sounds like |
|---|---|---|
| Authentic (perfect) | V to I | the end: the strongest close |
| Plagal | IV to I | “amen”, softer, at the end of hymns |
| Half | anything to V | a comma or a question: the phrase stops on tension |
| Deceptive | V to vi | you expect I and get its relative minor |
The Classical cadence demo in File > Demos plays two of them in a row: I, IV, V7, I, then vi, ii, V7, I. In the second phrase each root falls a fifth: A to D, D to G, G to C.
Roots that fall a fifth
A chord whose root is a fifth above the next one leads to it most strongly: V to I, ii to V, vi to ii. Chain them, and the harmony walks home around the circle of fifths: vi, ii, V, I is Am, Dm, G, C. Jazz lives on the last three, ii, V, I. The Circle of fifths demo goes through every chord of the key that way, as Baroque music does: I, IV, vii°, iii, vi, ii, V, I, or C, F, Bdim, Em, Am, Dm, G, C, each root a fifth below the one before (F to B is the one diminished fifth, so the chain stays in the key).
Some progressions you will hear everywhere:
| Numerals | In C | Where |
|---|---|---|
| I, V, vi, IV | C G Am F | countless pop songs |
| I, vi, IV, V | C Am F G | the doo-wop songs of the 1950s |
| ii, V, I | Dm G C | jazz standards |
| I, IV, I, V, IV, I | C F C G F C | the twelve-bar blues, spread over twelve bars |
| vi, ii, V, I | Am Dm G C | the circle of fifths, in songs like Fly Me to the Moon |
Minor keys
A minor key uses three forms of its scale (see Keys and modes), and its chords come from all three. Most music in minor keys plays the chord on the fifth note major, from harmonic minor, so that it has a leading tone and pulls home the way V does in major. In A minor:
| i | ii° | ♭III | iv | V | ♭VI | ♭VII | vii° |
|---|---|---|---|---|---|---|---|
| Am | Bdim | C | Dm | E | F | G | G♯dim |
Pop and jazz books number the third, sixth and seventh chords from the major scale, so C in A minor is ♭III; classical harmony books count them from the minor scale, so the same C is III. Settings > Harmony > Roman numerals in minor keys picks either (see Settings).
What often comes next
Pointing at a chord, holding it on the harmony keys or a keyboard, or hearing it while a song plays, frames the chords that often follow it, the most usual one the brightest. The hint next to the harmony keys names the move: “V to I: the strongest ending. The leading tone rises to the root.” Detailed, Short and Minimal, next to the hint, choose how much it explains.
These are not rules. They are the moves that centuries of music, and most pop songs, use most often, because of how chords pull on each other. Knowing them helps you guess what comes next in a song you are learning by ear, and choose on purpose when to surprise. Try it: play a demo, watch the harmony keys, and before each change guess which framed chord comes next.
Chords from outside the key, such as a ♭VII in a major song or a V7/V that leads to the dominant, are the subject of the next chapter, Chords from outside the key.