ABSTRACT
In order for a book to fulfil its instructive or didactic purposes, readers must be persuaded that the book’s content and its producer are reliable. Readers need to trust that the content is accurate and relevant and that its producer (author, compiler, printer, and/or publisher) has the authority to write or publish on the subject matter. 1 These persuasive efforts are enacted as much through visual as they are through verbal means. As Charles Kostelnick observes, elements of document design – including the visual language of images – play ‘a key role in establishing credibility – or lack of it.’ 2 Thus, he identifies establishing credibility, or ‘ethos,’ as one of the rhetorical functions of document design. Adrian Johns offers an important historical perspective on such a function: ‘Printed texts were not intrinsically trustworthy. When they were in fact trusted, it was only as a result of hard work.’ 3 Reliability was an important issue for early printed books on medical and astrological knowledge, for various reasons discussed in the previous chapters: because of discussions or even controversies about certain aspects of this knowledge, such as the epistemic value of images or the extent to which astrology can predict specific events; because of the competition among a multitude of different kinds of practitioners; and because of the new technology of print, which made it necessary for printers to build a reputation of reliability in order to survive as commercial entrepreneurs.
