In exploring what it is we know about taking part in conversation, or any other speech event (e.g. debate, interview, various types of discussions), we quickly realize that there is enormous variation in what people say and do in different circumstances. In order to begin to describe the sources of that variation, we would have to take account of a number of criteria. For example, we would have to specify the roles of speaker and hearer (or hearers) and their relationship(s), whether they were friends, strangers, men, women, young, old, of equal or unequal status, and many other factors. All of these factors will have an influence on what is said and how it is said. We would have to describe what the topic of conversation was and in what setting it took place. Yet, even when we have described all these factors, we will still not have analyzed the actual structure of the conversation itself. As language-users, in a particular culture, we clearly have quite sophisticated knowledge of how conversation works.