"Strawberry Fields Forever" was originally written on acoustic guitar in the key of C major. The recorded version is approximately in B 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 song begins with a flute-like introduction played on Mellotron, and involves a I–ii–I–VII–IV progression. The vocals enter with the chorus instead of a verse. It has "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 F7 chord (in A key).