There have been affirmations and criticism of Havelock's methods. His account of orality is based almost entirely on Homer, but the history of the Homeric text is not known, which forces Havelock to make claims based on assumptions that cannot fully be tested. The works of Milman Parry on Homer were instrumental in developing the orientation to his work, and the breakthrough sustained research which Havelock prepared. The "Parry-Lord thesis" was introduced by Rosalind Thomas, to clarify the import of this approach. Some later classicists argue that the poetic nature of Homer's language works against the very arguments Havelock makes about the intellectual nature of oral poetry. What he asserts as a definitive use of language can never be conclusively demonstrated not to be an accident of "metrical convenience." Homerists, like Platonists, found the book to be less than useful for the precise work of their own discipline; many classicists rejected outright Havelock's essential thesis that oral culture predominated through the 5th century. At the same time, though, Havelock's influence, particularly in literary theory, was growing enormously. He is the most cited writer in Walter J. Ong's influential "Orality and Literacy" other than Ong himself. His work has been cited in studies of orality and literacy in African culture and the implications of modern literacy theory for library science. "Preface to Plato" has remained continuously in print since its initial publication.