Abstract: Some recent arguments against the classical invariantist account of knowledge exploit the idea that there is a ‘knowledge norm’ for assertion. It is claimed that, given the existence of this norm, certain intuitions about assertability support contextualism, or contrastivism, over classical invariantism. In this paper I show that, even if we accept the existence of a knowledge norm, these assertability-based arguments fail. The classical invariantist can accommodate and explain the relevant intuitions about assertability, in a way that retains the idea that knowledge is the epistemic norm for assertion. When we consider the role of assertion as a conversational act, it becomes plausible that a subject's epistemic warrant to assert can be defeated even though she has knowledge. This defeasibility thesis is what allows the classical invariantist to accommodate and explain the kinds of intuitions on which assertability-based arguments depend.