1. A method for providing a cooperative conversational voice user interface, comprising: receiving an utterance at a voice input device during a current conversation with a user, wherein the utterance includes one or more words that have different meanings in different contexts; accumulating short-term shared knowledge about the current conversation, wherein the short-term shared knowledge includes knowledge about the utterance received during the current conversation; accumulating long-term shared knowledge about the user, wherein the long-term shared knowledge includes knowledge about one or more past conversations with the user; determining an intended meaning for the utterance, wherein determining the intended meaning for the utterance includes: identifying, at a conversational speech engine, a context associated with the utterance from the short-term shared knowledge and the long-term shared knowledge; and establishing the intended meaning within the identified context, wherein the conversational speech engine establishes the intended meaning within the identified context to disambiguate an intent that the user had in speaking the one or more words that have the different meanings in the different contexts; and generating a response to the utterance, wherein the conversational speech engine grammatically or syntactically adapts the response based on the intended meaning established within the identified context.