 Uttering a sentence is acting. This action can have various consequences, partly intended partly not. The fact that utterances as actions are embedded in a bigger scheme of interaction between humans has been put into focus recently (see, for example, Clark 1996). Another important aspect that has been highlighted recently is the fact that by uttering a sentence we can change the knowledge state of an entire group of agents, see Balbiani et al. 2008. After publicly announcing \(\phi\), \(\phi\) becomes common knowledge among the entire group. This idea sheds new light on a problem of Gricean pragmatics, where certain speech acts can only be successful if certain facts are commonly known between speaker and hearer. It is by means of an utterance that a speaker can establish this common knowledge in case it wasn’t already there.