The harmonic backbone of the blues

Two chords and the truth

Let’s start at the end. Or, more accurately, at “The End” by the Beatles, about 35 seconds into it, the “hold you, love you” part that goes into the guitar solos.

This is a loop of two chords, A7 and D7, the I7 and IV7 chords in the key of A. It isn’t a remarkable or unusual progression; you have probably heard it in a hundred other songs, or a thousand. It feels elemental, like, THIS IS ROCK AND ROLL. Or more accurately, THIS IS THE BLUES, but played faster, so it sounds more like rock. Either way, the I7-IV7 progression is one of the most common harmonic tropes in Anglo-American popular music. Would it surprise you, then, to learn that Western tonal theory is powerless to explain it? Especially when it’s accompanied by blues-style melody?