The previous chapters have shown how practical reasoning is used in arguments, but it will turn out to be vitally important to understand how it is used in explanations. It will even be shown at the end of this chapter how the same example of practical reasoning in a discourse can combine explanations with arguments. Hence, there arises the problem of building a model of explanation to reveal precisely how practical reasoning is used in explanations. The key to solving it, as will be shown in this chapter, is to broaden the study of practical reasoning to take into account not only its structure as a chain of reasoning, but also how that same kind of reasoning can be used in different ways in different communicative settings. An argument will be shown to be a response to a particular kind of question, while an explanation will be seen as a response to another kind of question.

Recent work in artificial intelligence has taken the approach that an explanation is best seen as a transfer of understanding from one party to another in a dialogue where one party is a questioner who asks why or how something works and the other party attempts to fulfill this request (Cawsey, 1992; Moore, 1995; Moulin et al., 2002). Recent literature in philosophy of science seems to be gradually moving toward this approach, but there is an open question of how it can be represented using a formal structure (Trout, 2002). Since explanations and arguments are sometimes hard to distinguish, the first step is to provide some way of representing the distinction between them in their formal structure. In this chapter, the Why2 Dialogue System is presented as a formal model showing how the difference between argument and explanation resides in the pre- and post-conditions for the speech act of requesting an argument and the speech act of requesting an explanation. It is an extension of earlier dialogue systems (Walton, 2004, 2007a, 2011).