[1] His studies of the manuscripts of Geoffrey Chaucer and William Langland were especially important, and his 1978 article "The Production of Copies of the 'Canterbury Tales'" was described as "seminal".
Among his important individual achievements are the dating of the Oxford MS. of The Song of Roland and his work on early manuscripts of the Canterbury Tales (with Ian Doyle), still considered a standard.
[1] His Lyell Lectures at Oxford discussed the prosopography of English scribes[1] and focussed on how they wrote, rather than on terms for identifying scripts, and proved him an erudite and entertaining lecturer.
He compiled a catalogue of Keble College's medieval manuscripts which was published in 1979 by Scolar Press, London.
[6] Parkes was elected to the Comité international de paléographie latine in 1986 and was a corresponding fellow of the Medieval Academy of America from 1992.