This is a difficult book and to minimize the difficulties we must try to give as many definitions as possible. Discourse is a language unit analysable with the same methods as the sentence but larger than the sentence. For example a question is a sentence the answer to that question is a sentence but the question and the answer taken together within the same context are a discourse. The great problem is that linguists cannot usually handle discourse. They can only handle sentences. And the top example of linguists in that context is N. Chomsky. In consequence the discourse analyst must get accustomed to operate within different dimensions. This book suggests dimensions it does not impose them. And it must be said strong and clear that the most important factor in discourse is presupposition. Now you must have it very clear in your mind that presuppositions are concepts of logic not of grammar. Therefore with discourse we are slowly or more rapidly moving away from conventional grammar and getting closer to different ways of looking at language. It is only after having studied this book that you can begin to understandif you have some intelligencethat discourse moves into various branches of logic rather than within what antiquity called grammar. The future lies with discourse and the constraints are the restrictions we impose on the text which are not exactly restrictions of grammar though sometimes they may coincide. The only thing I can say is: Forget grammar! Learn the principles and the restrictions of logic! Good luck.