There are two broad classes of Chord Function:
- To establish key center and tonality (major, minor, blues, etc).
- To create harmonic motion or tension.
Here, for example, is a commonly-used chord progression in the key of C…
Listen and notice four things:
- The first C chord establishes the key center C and major-ness of the piece.
- The chords that follow create a chain of harmonic motion that leads naturally from chord to chord.
- Each chord has a unique sound-feeling, a unique harmonic tension with respect to the key center C.
- The harmonic motion is eventually resolved with the final C chord.
This analysis is more than mere “theory”. It captures the organic essence of how humans naturally experience and enjoy music. Don’t fuss about the details right now. It is sufficient to understand that chord progressions create forward motion and typically follow logical paths based on a small number of simple formulas for harmonic tension and resolution.