Easy Two Shape Chord Progression! In the key of C, the 1 4 5 chord progression refers to the chords built on the first, fourth, and fifth notes of the C major scale: C, F, and G, respectively. These three chords are also known as the I, IV, and V chords in the key of C, and they form the basis of many popular songs in various genres, including rock, blues, country, and pop. The 1 4 5 chord progression is commonly used as a harmonic framework for creating melodies, solos, and lyrics in a song. Th