At first called "Scrambled Eggs," the title of this touching song which has become one of the most popular tunes of all time was thankfully soon changed upon the release of the album Help! in 1965. It was the first tune sung solo by a member (Sir Paul McCartney) of the Beatles group, and also explored the resources of the multi-track studio, primarily by the addition of a string quartet.
The song is a portrait of the emotions of a man recently rejected by his lover for an insensitive remark, and who is now searching for a spiritual place of reassurance: "I said something wrong, now I long for yesterday."
The verse opens with a large arching phrase that covers seven measures. The emotional tension is created by a series of resolutions of a non-harmonic tone into a harmonic tone -- for example, the first word "Yesterday" sung against an F major chord, resolves a G note to an F; on the words "...far away" on a D minor chord, the notes are an E resolving to a D; on "...here to stay" on an F chord, B flat moves to an A. Between these points the melody line consists mostly of lyrical scale runs ending in a plagal (Amen) cadence.
The bridge modulates to the relative minor key (D minor) by a beautiful harmonic touch: instead of simply repeating an A dominant seventh chord ("Why she..."), the collaborators recapitulate the chords from the second measure of the verse (E minor seventh, A seventh) but place them over a pedal point on A. This subtle choice creates a tonal richness that suggests an approaching Dorian mode which is changed to a pure Aeolian (minor) in the next measure.
In this bridge, the melody hangs around in the upper register. There is a series of sighs, or sublimated pleas ("Why she had to go I don't know she wouldn't say"), marked with dynamic crescendos and diminuendos before the verse returns and concludes with the same seven measure melody.
A simple, hummed two-measure coda seems to sum up the harmonic flow of the tune: the tonic chord (F over C) is heard for two beats, the second measure "modulator" (G over B) for two beats, and the plagal cadence fills the last measure. Amen.