Ben Weiss, Curator of Rare Books at the Burndy Library of MIT's Dibner Institute for the History of Science and Technology:
Ben Weiss: Brad DeLong's Website: DeLong's Ignorance Corrected!: "First off, I love your blog, and read it avidly; many thanks for the wide learning and elegant argument... http://www.j-bradford-delong.net/movable_type/2005-3_archives/000643.html
...I don't know if you go through your comments section, so I thought I would also email this to you, as there is a bit of economic history buried in the response. A wonderful post, and a wonderful Machiavelli quotation, but I'd like to take a bit of issue with the comment about libraries in the fifteenth and sixteenth centuries --- and, yes, I know that's really the point of the post.
The general point that libraries were fewer and smaller before the advent of printing than after is basically true. So is the fact that manuscripts were harder to come by and more expensive than printed books, but Brad's comment that "the idea that a mere mortal--a disgraced ex-Assistant for Confidential Affairs to the Republic of Florence--might have a personal library would have been absurd even half a century earlier," is far too stark. In the early Middle Ages libraries really were the province of "kings, sovereign princes, and abbots", but there was a steady increase in both literacy and the number of books in circulation during the later Middle Ages. This was especially true in cities: notably in Northern Italy, but also in France and what would become Germany. By the late fourteenth century, a bureaucrat with literary tastes like Machiavelli would almost certainly have had personal copies of a large number of his favorite books, and, if he were wealthy enough, possibly even a little study (a "studiolo") in which to read them.
Over the course of the thirteenth and fourteenth centuries the book trade underwent a dramatic shift as the primary center of manuscript copying moved from monastic houses to commercial scriptoria, often in university towns. (Richard and Mary Rouse have written a very important, if slightly exhausting, two-volume history of the commercial book trade in Paris: Manuscripts and their makers: commercial book producers in medieval Paris, 1200-1500 (Turnhout, 2000).) This was both fostered by and, in turn, fostered an increase in demand for personal copies of university texts. In Paris, as in places like Vienna, Padova, and Krakow, there was an active market in both new and used manuscripts, and, in addition, many scholars (especially in Italy) copied texts out themselves.
But perhaps the most important piece of evidence of the increasing demand for books before Gutenberg is the invention of printing itself. Gutenberg was not just experimenting for the sake of experiment. He was responding to, if not an explicit demand, to a perceived opportunity. It's important to remember that the printing press was not devote to making a new type of object --- early printed books are exactly the same in form and layout to manuscripts --- but to make more of a commodity that already existed.
With thanks, and all best wishes...