Chapter 5 fits the knowledge rule of assertion into the functionalist picture. We ask the question of why assertion should be governed by the knowledge rule, look at some proposals from the rule first camp, due, respectively, to Bach and Hindriks on the one hand and Douven on the other, and show that they remain unsatisfactory. We then offer a functionalist account of the status of the knowledge rule of assertion as well as a functionalist rationale for it.