The Japanese change-of-state tokens a and aa in responsive units

This paper investigates Japanese particles a and aa in responsive turns. Although both of these tokens display change-of-state of the speaker's cognitive state, they mark different types of epistemic stance. Through analysis of collocating items and sequential environments, it is shown that by producing an a-prefaced response, speakers display a change of state from not-knowing to knowing, receipting the information as new and thereby exhibiting surprise. By contrast, with an aa-prefaced response, speakers display a change of state but simultaneously show that they have previous knowledge of some parts of the informing. To demonstrate the knowledge, an aa-speaker often extends a sequence by providing a piece of information that has not been mentioned in the conversation. Although infrequently, a and aa sometimes co-occur in one utterance, in the order of a followed by aa, working together as resources to register the change of state and display understanding.