Abduction and Conversational Implicature (Extended Abstract)

In this abstract, we first consider abduction in human dialogues. Two different types of abduction, objective abduction and subjective abduction, are introduced and formulated using propositional modal logic. We next formulate conversational implicature in the same logic and contrast it with abduction in dialogues. According to our formulation, abduction uses private belief of a reasoner, while conversational implicature relies on common knowledge between participants in conversation. The results characterize how hearers use abduction or conversational implicatures to figure out what speakers have implicated and show how two commonsense inferences are distinguished.