A remarkable day's work at Abbey Road, dominated by Paul and perfectly illustrating this young man's mastery of three different styles of musical composition and singing. It was on this day that he continued recording 'Yesterday', the song which, by public acclaim, will always rank among his best.
But it was more than just a great tune. It was also trendsetting recording (June 17) employment of a string quartet for the first time on a Beatles record introducing a new era: the group would continue to utilise strings and orchestras on a regular basis to the end. Typifying their working relationship, Paul assisted George Martin with his score, adding little touches here and there.
Two takes of 'Yesterday' were recorded by Paul alone, acoustic guitar and vocal, between 7:00 and 10:30 pm and then the four-track tape was set aside for completion on the 17th. (Newspaper of the time made a fuss of the factthat none of the other Beatles played on the recording, and that they weren't even present in the studio, but the session tape reveals that George, if not John and Ringo, were certainly there.)
What makes Paul's recording of 'Yesterday', the supreme melodic ballad, all the more remarkable, is that it directly followed the taping of 'I'm Down', a quasi-soul/rock and roll song delivered by Paul in the most larynx-tearing, cord-shredding style. This was started and completed in seven takes during a 2:30-5:30 afternoon session along with the first song to be taped this day, Paul's folk-rock 'I've Just Seen A Face', begun and finished in six takes.
Source: The Complete Beatles Chronicle by Mark Lewisohn