The research aims to study the communicative function of und so in authentic German discourses from the daily life. There is a group of language expressions such as und so, oder so and oder so was, which are used in order to refer to specific knowledge in the mental sphere of the listener, without speaking about this knowledge in details and also without neglecting it. The speaker considers the common knowledge with the listener as a precondition for the communication. This common knowledge will be categorized in this research as presupposition and the language expressions, which depend on this common knowledge as precondition, are called markers of presupposition. Presupposition is classified then as distinguishable type of knowledge like these types classified by Ehlich and Rehbein. The research depends on the analysis method of the functional pragmatic and springs from the functional pragmatic consideration of presupposition as social phenomenon, which is gained from the society as Rehbein assures and which is not only explainable through traditional consideration of presupposition as phenomenon of logic and semantic.
The analysis of und so in the German discourses leads to classification of knowledge in discourse in: main knowledge, parallel knowledge and alternative knowledge. The parallel knowledge is more over classified in side-knowledge and collateral knowledge. Und so expresses the referring of the Speaker to the collateral knowledge.