Chord Progressions and Roman Numerals

A chord progression is a sequence of chords played one after another. Almost every song you know is built on one. To understand why some progressions sound so satisfying, you first need to know where the chords come from: the key.

Diatonic chords

Diatonic chords are the chords built on each note of a scale using only notes from that key. Stack a triad on every step of the major scale and you get seven chords, each with its own quality. In a major key those qualities are always the same: I major, ii minor, iii minor, IV major, V major, vi minor, and vii° diminished.

We label them with Roman numerals. An uppercase numeral means a major chord, a lowercase numeral means a minor chord, and the little circle (°) means diminished. Here are the seven diatonic chords in the key of C major:

Tension and home

Two chords do most of the work. The I chord is the tonic: it feels like home, the place of rest. The V chord is the dominant: it feels unresolved and pulls strongly back to the tonic. That push and release between V and I is the engine behind countless progressions.

Famous progressions

• I–V–vi–IV: the backbone of countless pop songs.
• I–IV–V: the heart of blues and rock.
• ii–V–I: the classic cadence at the core of jazz.

Notice how each one leans on that V-to-I pull to reach a sense of arrival. Play them below. The progression player works in any key, so you can hear the same numerals in different letters and confirm that the pattern, not the exact notes, is what your ear recognises.

Songs are not really made of chords, they are made of relationships between chords. Learn the numerals once and you can play the same progression in every key.