 The logical toolbox for epistemic logic with communicative updates is called dynamic epistemic logic or DEL. DEL started out from the analysis of the epistemic and doxastic effects of public announcements (Plaza 1989; Gerbrandy 1999). Public announcement is interesting because it creates common knowledge. There is a variety of other kinds of announcements—private announcements, group announcements, secret sharing, lies, and so on—that also have well-defined epistemic effects. A general framework for a wide class of update actions was proposed in Baltag et al. 1999 and Baltag and Moss 2004. A further generalization to a complete logic of communication and change, with enriched actions that allow changing the facts of the world, is provided in Benthem et al. 2006. A textbook treatment of dynamic epistemic logic is given in Ditmarsch et al. 2006.