Every meaningful message contains new information, or at least information meant by the speaker to be new for the hearer, embedded in old information. Every message aims at communicating something new. If I were to say now two and two is four, that would be meaningless, because that sentence contains only old information and nothing new is communicated. On the other hand, a sentence that contains only new information e.g. suddenly he got extremely scared cannot be understood, it cannot be assimilated to previous knowledge. The quite normal sentence I met your brother yesterday contains as new information that a certain meeting has taken place at a certain moment. There is also old information: knowledge shared by the speaker and hearer which is presupposed to be true. The presupposed information in this case is that the hearer has a brother. A linguist who has recently studied verbal communication and semantics in the framework of old and new information is Chafe (1970, 1972). Related distinctions are topic and comment, given and new, theme and rheme (Halliday, 1967, 1970) presupposition and focus (Chomsky, 1971).