Murrinhpatha, an Aboriginal language of northern Australia, has an initial k-alternation in verbs that has hitherto been resistant to grammatical analysis. I argue that k- does not encode any feature of event structure, but rather signals the speaker’s epistemic primacy over the addressee. This authority may relate to concrete perceptual factors in the field of discourse, or to socially normative authority, where it asserts the speaker’s epistemic rights. These rights are most salient in the domains of kin, country and totems, as opposed to other topics in which speakers are habitually circumspect and co-construct knowledge. My analysis of the k-alternation thus brings together the typology of epistemic grammar (Evans, Bergqvist, & San Roque, 2018a, 2018b), and a sociolinguistic perspective on stance (Jaffe, 2009).