Chord progressions are the basis of harmony in songs and there are many common or standard progressions that are useful to know.

(a chord progression is simply a sequence of chords: one chord after another.)

Chord progressions are often thought about in terms of the chord roles in a particular key, rather than the exact chords played.

For example, we talk about a “1 4 5” progression (or “I IV V“) rather than a “C F G” progression, because playing the chords with these scale degrees will produce the same characteristic sound in every key.

There are music theory rules for what chords can or should follow