Chord progressions

A chord progression is a sequence of chords. Some sequences recur so often that knowing a handful gives you a way into a huge amount of music.

They are written in Roman numerals so they work in any key.

I – V – vi – IV

1. CITonic
   →
2. GVDominant
   →
3. AmviTonic
   →
4. FIVPredominant

Probably the most used progression in modern popular music. It works because it never fully rests: the V leads somewhere, the vi is a soft arrival that is not quite home, and the IV pushes back round to the start. It loops indefinitely without ever sounding finished.

Rotations of the same four chords are equally common: vi–IV–I–V and IV–I–V–vi are the same cycle entered at a different point.

ii – V – I

1. DmiiPredominant
   →
2. GVDominant
   →
3. CITonic

The backbone of jazz harmony, and the clearest possible statement of the functional circuit: predominant, dominant, tonic. Usually played with sevenths — Dm7, G7, Cmaj7.

Its roots move by descending fifths (D → G → C), which is the strongest root motion in tonal music.

I – vi – IV – V

1. CITonic
   →
2. AmviTonic
   →
3. FIVPredominant
   →
4. GVDominant

The "fifties progression". Doo-wop, early rock and roll, and a great many ballads since. Unlike I–V–vi–IV it ends on the dominant, so each loop pushes back to the top.

The twelve-bar blues

Twelve bars using just I, IV and V:

I  I  I  I
IV IV I  I
V  IV I  I

In practice all three are usually dominant sevenths — I7, IV7, V7 — which is harmonically unusual and part of what makes the blues sound like itself: chords that "should" resolve, sitting still instead.

Descending fifths

Roots falling by a fifth each time: vi – ii – V – I, or extended further back to iii – vi – ii – V – I.

Each chord is the dominant of the next, so the sequence pulls forward relentlessly. It underpins a large amount of Baroque music and most jazz standards.

Why so few patterns

Because function constrains the options. Progressions that move tonic → predominant → dominant → tonic sound purposeful, and there are only so many ways to arrange seven chords into three functional slots.

That is also why substitution is so productive: swap any chord for another with the same function and the progression still works but sounds different.