In a work with implications for the electronic age, Ivan Illich explores how revolutions in technology affect the way we read and understand text. Examining the "Didascalicon" of Hugh of St Victor, Illich celebrates the culture of the book from the 12th century to the present. Hugh's work, at once an encyclopedia and guide to the art of reading, reveals a 12th-century revolution as sweeping as that brought about by the invention of the printing press and equal in magnitude only to the changes of the computer age - the transition from reading as a vocal activity done in the monastery to reading as a predominantly silent activity performed by and for individuals.