Lennon commented on "I'll Be Back":
“A nice tune, though the middle is a bit tatty. My variation of the chords in a Del Shannon song Runaway.”
McCartney claims it was co-written.
The song was to have been recorded in ¾ waltz time. However it was changed to 4/4 when Lennon decided it was too difficult for him to sing.
Says Beatle scholar Tim Riley:
“With a typical timidity, John is asking for another chance after backing out, and his discomfort seeps into the music Both verse and bridge waddle along so dodgingly between major and minor that at the end instead of giving the listener a firm decision on the matter, the song simply fades out alternaternating between the two as any hope of resolution is left dangling in the air. Lennon has never before been this honest about being this indecisive.“
The track is a melancholy essay in major/minor uncertainty mirrored in the emotional instablity of its lyric. It has a loose Spanish flavor to the accoustic backing and Lennon vocal is naked. The octaves that emphasize “oh, yeah!” to conclude both the refrain and the bridge reach down to the foundation of Lennon’s vocal range.
It is impossible to actually tell what is the verse and what is the chorus, or just how many different bridges there are. The song is a significant achievement of this period from a melodic and harmonic point of view. It defies effective categorization as either pop-rock or medium tempo ballad.
The inclusion of two separate bridge sections in the song is formally unique and most likely dictated by text considerations. But the song’s most remarkable qualities are concentrated in the verse: the elegant simplicity of it melody; its rich, modally-tinged harmonic variety; and the poignant lyrical delivery that lends a new seriousness and pathos to an otherwise standard lament. It’s modally enriched lyricism.
Songs like this are considered “popular folk songs” because they demonstrate a certain restrain in approach and a lack of intensity not characteristic of the Beatles’ earlier work.
The narrator is talking about about the possibility of betrayal and is, significantly, one of the bluest of early Beatle songs, in feeling if not form.
Professor Ken Womack writes that the speaker, supported by a clutch of bristling acoustic guitars, offers what appears to be a fairly routine dirge about the emotional traumas of lost love. Yet, rather interestingly, the speaker learns an excruciating lesson about the fleeting nature of romance.