Chord Progression

A chord progression is the harmonic skeleton of a song — the order in which chords change as time moves forward. In Western popular music, a small handful of progressions cover most of the canon. The I-V-vi-IV progression (C-G-Am-F in C major) is the famous "four-chord song" that fits "Let It Be", "No Woman No Cry", "Don't Stop Believin'", and hundreds of others. The 12-bar blues is a I-IV-V variant that anchors blues, rock and roll, and most early jazz.

Chords are built from scales, and they have functions. The I chord (tonic) is home. The V chord (dominant) creates tension that wants to resolve back to I. The IV chord (subdominant) provides contrast without strong tension. The vi chord (relative minor) introduces emotional shading. Once you can hear these functions, you can predict what chord is likely to come next — and intentionally subvert that expectation when you want surprise.

Modal interchange (borrowing a chord from a parallel scale), secondary dominants (a temporary V chord of a non-tonic), and key changes all extend the toolkit. But the foundation is the same: chords have function, function creates expectation, and great songwriters use both expectation and surprise to make harmonic motion feel inevitable in retrospect.