We always have a good idea of what is coming next, so that we are seldom totally surprised. We may be partly surprised; but the surprise will always be within the framework of something that we knew was going to happen. And this is the most important phenomenon in human communication. We make predictions –not consciously, of course; in general, the process is below the level of awareness– about what the other person is going to say next; and that’s how we understand what he or she does say. […] How do we make these predictions? The first step towards an answer is: we make them from the context of situation. The situation in which linguistic interaction takes place gives the participants a great deal of information about the meanings that are being exchanged, and the meanings that are likely to be exchanged.
Michael A. K. Halliday y Ruqaiya Hasan, Language, Context and Text: Aspects of Language in a Social-Semiotic Perspective, Oxford, Oxford University Press, 1989, 2ª ed., pp. 9-10