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Samples in periodicals archive:
Chapter 2, "Inside the Gamut: The Major Sixth in Guido of Arezzo and Hermannus Contractus," examines the roles played by the major sixth in the theories of Guido and Hermann.
George Martin, The Beatles' producer, argued with Lennon and McCartney about the major sixth chord that ends the song.
As such they are quite abstract, built in turn from a minor third, fourths and fifths, and a major sixth.