Four chords: I - V - vi - IV progression in G major

I - V - vi - IV

Four chords is a sunny progression, shown here in G major (tonic G) with the degree sequence I - V - vi - IV.

I-V-vi-IV is probably the most-used progression in contemporary pop, so much so that it's become a running joke (the famous "Axis of Progression"). It starts on the tonic, moves through the dominant (V), slides onto the relative minor (vi), and comes home by way of the fourth degree (IV) -- an emotional arc that rises and falls in a way the ear finds very natural.

See G major on the circle of fifths