Abstract
I propose the Shared Presupposition Norm of Joking (SPNJ) as a constitutive norm of joke-telling. This norm suggests that a person should only tell a joke if they believe their audience shares the presuppositions—both explicit beliefs and implicit inferential connections—upon which the joke turns. Without this shared understanding, the audience would lack the necessary comprehension to appreciate the joke. I defend this norm in an analogous way to Williamson’s defense of the Knowledge Norm of Assertion by demonstrating that it explains a number of patterns of joking behavior. If SPNJ is indeed a constitutive norm of joking, it provides an epistemological foothold. Jokes function as conversational explicatures serving an epistemically diagnostic function, revealing implicit and perhaps disavowed inferential dispositions of the joking community. This norm does not teach us about the subject matter of the joke, but instead illuminates the language games of the joke teller and audience.