What Is a Chord Progression? A Few Sequences Doing Most of the Work

Chords built on the notes of a key have conventional functions, describing their relationship to the home chord. The tonic is home and sounds settled. The dominant, built on the fifth degree, contains notes that pull strongly towards the tonic, particularly the note a semitone below it, so it creates tension seeking resolution. The subdominant, on the fourth degree, moves away from home without the urgency of the dominant. Minor chords built on other degrees supply colour and substitute for those functions. A progression is therefore a path through departure and return, and the listener tracks it without any training because exposure teaches the expectations. That is why the same three chords in different orders feel different, why a progression ending on the dominant feels unfinished, and why a song can generate momentum simply by delaying the return home. Numbering the chords by scale degree, conventionally with roman numerals, allows a progression to be discussed independently of key, which is how musicians actually talk about them.

A handful of sequences appear across enormous numbers of songs and each has a characteristic feel:

• •The twelve-bar blues, a fixed pattern of tonic, subdominant and dominant over twelve bars, which underpins blues, early rock and roll and a great deal of what followed
• •The one four five, the simplest complete departure and return, which is most of folk, country and early rock
• •The fifties progression, adding a minor chord on the sixth degree, which is the sound of doo-wop and a very large number of ballads since
• •The four-chord loop on degrees one, five, six and four, which is the pattern a well-known comedy routine used to play dozens of hit songs consecutively
• •The two five one, the backbone of jazz harmony, which is a compressed and strongly directed route home
• •Modal and static progressions that avoid the dominant altogether, which produce the floating quality of much folk, film and ambient music

The recurrence has an explanation beyond imitation. The number of chords that fit comfortably in a key is small, the functional relationships constrain which orders sound directed rather than arbitrary, and the requirement that a listener follow the structure without effort rules out much of the remaining space. Beyond that, a familiar progression is a feature rather than a defect, since it frees attention for melody, rhythm, lyric, timbre and performance, which is where most of the distinctiveness of a song actually lies. Two songs on the same progression rarely sound alike, because the elements that differ are the ones listeners attend to. Musicians also exploit familiarity directly, setting up an expected progression and breaking it at a chosen moment, which is only available because the expectation was established. The situation is comparable to metre in poetry, where a shared framework makes variation legible rather than preventing it.

Copyright law does not protect chord progressions as such, treating them as building blocks too basic for anyone to own, in the same way that a scale or a rhythm cannot be owned, and courts have stated this repeatedly. That is fortunate, since protecting them would make writing songs legally hazardous. What can be protected is a specific combination of melody, harmony and rhythm that amounts to original expression, and litigation turns on whether the resemblance between two works goes beyond the shared building blocks. Several prominent cases have been criticised by musicologists for coming close to protecting elements that should be free, and an appellate decision in 2020 concerning a well-known descending sequence explicitly reaffirmed that common progressions are not protectable. The practical position for a songwriter is that using a standard progression is safe and that combining it with a melody closely resembling an existing one is not, which is a clearer line than the coverage of individual cases suggests.

Chords have conventional functions relative to home, so a sequence is a path of departure and return that listeners track without training, which is why the same chords in a different order feel different. A handful of sequences recur because the space of ones that sound directed is small and familiarity frees attention for melody and performance. Progressions themselves are not protected by copyright.