R.R. Bolgar, The Classical Heritage and Its Beneficiaries (p. 9):
The works of a number of major writers have been examined from this point of view, and we are in a position to form a clear picture of the classical reading of Alcuin, John of Salisbury, Dante, Chaucer, Rabelais, Ronsard, Spenser, Shakespeare, and Ben Jonson, to name only a few. Caution, however, is very necessary. If a man quotes a passage, he has read it; but we must not assume that he has read the work in which it occurs. Quotations were often taken second-hand from grammar books. The researches of C.K. Ullman have revealed that anthologies contributed largely to the classical knowledge of medieval scholars; and everybody has been aware for a long time now that many of the Renaissance pundits, like Rabelais and Ben Jonson, similarly derived the greater part of their erudition from popular handbooks. Nor can we accept without reserve the claims made by individuals that they or others had read certain classical authors, for no medieval or Renaissance writer is altogether free from the minor vice of exaggeration.
