His doctoral thesis on Elizabethan madrigals was published in 1962 and was notable for contextualizing them in the preceding Italian madrigal tradition. He maintained an interest in the English madrigal composer William Byrd throughout his career, and wrote several influential monographs on his work. He wrote a widely popular book on the Beethoven string quartets in the style of Donald Francis Tovey. With his wife, Vivian Kerman, he wrote the widely used textbook, "Listen", first published in 1972 and now in its 7th edition co-authored by Gary Tomlinson. In 1985 he published his history and critique of traditional musicology, "Contemplating Music: Challenges to Musicology", which argued that the intellectual isolation of musical theorists and musicologists and their excessively positivistic approach had hampered the development of serious musical criticism. Described in "The Grove Dictionary of Music and Musicians" as "a defining moment in the field", the book has been credited as helping to shape a "new musicology" that is willing to engage with feminist theory, hermeneutics, queer studies, and post-structuralism.