A chord progression is chords in order. Name them by number instead of by letter and the same progression works in every key, which is why session players and bandleaders talk in Roman numerals.
Roman numerals
Build a triad on each degree of the scale and number them: I on the first, IV on the fourth, V on the fifth. Upper case marks a major chord, lower case a minor one. I is the tonic, IV the subdominant, V the dominant. In C major, I–IV–V is C, F and G; in G major the same numerals give G, C and D.
Progressions you will hear everywhere
| Progression | In C | Where it lives |
|---|---|---|
| I–IV–V | C F G | The three-chord core of countless songs |
| I–V–vi–IV | C G Am F | Called extremely common; a pop staple |
| ii–V–I | Dm G C | The jazz turnaround |
| I–ii–V | C Dm G | IV swapped for its relative minor, ii |
Any chord can take a seventh or other added notes without losing its place in the progression: ii7–V7–Imaj7 is still a ii–V–I.
The twelve-bar blues
The most common blues form is twelve bars long and built mostly on I, IV and V. In the version that became standard, the last four bars run V–IV–I–I; in the earliest form the dominant was repeated in bar twelve.
| Bars | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| 1–4 | I | I | I | I |
| 5–8 | IV | IV | I | I |
| 9–12 | V | IV | I | I |
Cadences: how a phrase ends
A cadence is the chord motion that closes a phrase. There are four main kinds.
| Cadence | Motion | How it sounds |
|---|---|---|
| Authentic | V (or another dominant chord) to I | Closed; virtually obligatory at the end of a tonal piece |
| Half | Ends on V | Open, a comma that calls for more |
| Plagal | IV to I | Softer; the "amen" at the end of a hymn |
| Deceptive | V to a chord other than I, often vi | The ending you expected, swerved |
Sources
Every date, name, tempo and origin on this page comes from these pages, read on 2026-10-24.