A chord on its own is a color; a progression is what makes the music go somewhere. Most music leans on a handful of them, and they are easiest to learn the way musicians write them: by number rather than by name.
Why are chord progressions written in Roman numerals?
Number the notes of the scale 1 to 7 and build a chord on each: in C major that gives C, Dm, Em, F, G, Am and B°. A Roman numeral names a chord by that number, upper case for major and lower case for minor, so I–IV–V–I means the chords on the 1st, 4th and 5th notes. In C that is C–F–G–C; in G it is G–C–D–G. The numerals do not change.
Common chord progressions
| Progression | In C | In G | Where you hear it |
|---|---|---|---|
| I–IV–V–I | C–F–G–C | G–C–D–G | Hymns, folk songs, and many first piano pieces |
| I–V–vi–IV | C–G–Am–F | G–D–Em–C | Pop and rock songs, especially since the 1990s |
| I–vi–IV–V | C–Am–F–G | G–Em–C–D | Ballads of the 1950s |
| ii7–V7–Imaj7 | Dm7–G7–Cmaj7 | Am7–D7–Gmaj7 | Jazz standards |
| I7–IV7–V7 | C7–F7–G7 | G7–C7–D7 | The 12-bar blues, which is built on these three chords, and the rock and roll that grew out of it |
Once you know a progression by number, moving it to another key means finding the same numbers in the new scale. Try I–V–vi–IV in C, then in G: the shape under your hands moves, and the progression still sounds like itself.
How do you play a chord progression smoothly?
Playing every chord in root position makes the hand jump. Pianists keep the notes two chords share and move the others as little as they can, which means playing some chords inverted: the same notes in a different order. C to G becomes C–E–G to B–D–G, where the G stays and two fingers move one step.