Ed Sheeran successfully defended his copyright court case, what is chord progression and why do so many songs use it?

Question

I watched a video where he demonstrated that many songs use the same tune / Chord progression (?). What is chord progression and why was the one in question essentially uncopyrightable?

In: 531

Answer 1

In pure theory the idea of copyrighting chord progressions is ludicrous:

Tonic-Subdominant-Tonic-Dominant-Tonic is the basic form of almost every rock & roll song from 1956-1962.