Active logic applied to cancellation of Gricean implicature

Using a simple example of a dialog with an impli-cature that arises part way through and then is later retracted, we discuss how Gricean maxims and nonmonotonicity may relate to each other and to a computational treatment of implicature. In eeect we seek to track reasoning along Gricean lines over time. We present our own computational approach to this, giving an implementation in the formalism of active logics.