In this paper we will argue that the analysis of lies, fallacies, and misunderstandings requires a complex model including a heterogeneous common ground based on reportative and situational evidence (cf. Farkas & Bruce 2010) and two additional layers, beliefs and objective facts. Lies can be defined by using the concept of reportative evidence, i. e. there is a contrast between an utterance and the utterer’s beliefs. Fallacies arise if a person is mistaken with regard to the situational evidence, i. e. there is a contrast between her beliefs and the objective facts. Misunderstandings, again, refer to reportative evidence, i. e. there is a contrast between the intended meaning of an utterance and the way it is understood by the hearer. Whereas the analysis of liesproves that the common ground is based on evidence and not on mutual belief, the analysis of fallacies and misunderstandings shows that both its situational and its reportative part have to split up into one part that is clearly fixed and another part that is open to interpretation and thus endangered by these communication failures.