Each one occupies more or less one bar, and each one comes with a chord: F7, E♭, B♭, and F7 again. The “Hey Jude” loop is built from four phrases.
The blue arrows show the roots of the I-♭VII-IV-I chord progression. The right diagram shows it on the circle of fifths. The left diagram below shows F Mixolydian on the chromatic circle.
If you play I, ♭VII, and IV, you’re going to recognize many iconic rock and pop songs. B-flat is the fourth note in F Mixolydian, so the chord built on it is called the IV chord.E-flat is the seventh note in F Mixolydian, so the chord built on it is called the ♭VII (the flat is there to distinguish E-flat from the “natural” seventh you’d get in the major scale, which here would be E natural.).F is the first note in F Mixolydian, so the chord built from it is called the I chord.The chord structure is the old classic rock standby, I-♭VII-IV-I. The progression comes from the Mixolydian mode, which is as defining for rock as diatonic major is for classical.
