At the opening of the fourth book, Castiglione laments that many of the courtiers present in the conversations have passed away. The legacy of these courtiers has been preserved under the governance of the new Duchess, Eleanora Gonzaga. Signor Ottaviano is late, but when he arrives, discussion resumes. Elegant dress and manners, Ottaviano asserts, make men “effeminate” (284). The aim of the courtier is to serve his ruler, and “falsehood” to be avoided (285). Ottaviano counsels that the courtier should seek to spur his prince to virtue by displaying it himself. Signor Gaspare protests that men are born either virtuous or not, and cannot learn the virtues Ottaviano describes. Ottaviano contends that habit, not nature, determines virtue, and like a “good farmer,” the courtier can cultivate it (291). To Gaspare’s critique that some men knowingly commit evil, Ottaviano returns: ”true pleasure is always good” (292). Pietro Bembo maintains that the ignorant cannot distinguish good from evil. Ottaviano claims that true knowledge will disabuse the ignorant of vice, and “temperance destroys all seditious enemies” (294).

Signor Gaspare asks which is the happier form of government, rule by a prince or a republic? Ottaviano answers a prince, because as in nature, the mind rules the body, so the monarch rules the many.