 The song was originally written on acoustic guitar in the key of C major. The recorded version is approximately in B-flat major; owing to manipulation of the recording speed, the finished version is not in standard pitch (some, for instance consider that the tonic is A). The introduction was played by McCartney on a Mellotron, and involves a I – ii – I – ♭ VII – IV progression. The vocals enter with the chorus instead of a verse. In fact we are not "taken down" to the tonic key, but to "non-diatonic chords and secondary dominants" combining with "chromatic melodic tension intensified through outrageous harmonisation and root movement". The phrase "to Strawberry" for example begins with a somewhat dissonant G melody note against a prevailing F minor key, then uses the semi-tone dissonance B ♭ and B notes (the natural and sharpened 11th degrees against the Fm chord) until the consonant F note is reached on "Fields". The same series of mostly dissonant melody notes cover the phrase "nothing is real" against the prevailing F # 7 chord (in A key).
