How to Agree without Understanding Each Other: Public Announcement Logic with Boolean Definitions

Malvin Gattinger
(Bernoulli Institute, University of Groningen)
Yanjing Wang
(Department of Philosophy, Peking University)

In standard epistemic logic, knowing that p is the same as knowing that p is true, but it does not say anything about understanding p or knowing its meaning. In this paper, we present a conservative extension of Public Announcement Logic (PAL) in which agents have knowledge or belief about both the truth values and the meanings of propositions. We give a complete axiomatization of PAL with Boolean Definitions and discuss various examples. An agent may understand a proposition without knowing its truth value or the other way round. Moreover, multiple agents can agree on something without agreeing on its meaning and vice versa.

In Lawrence S. Moss: Proceedings Seventeenth Conference on Theoretical Aspects of Rationality and Knowledge (TARK 2019), Toulouse, France, 17-19 July 2019, Electronic Proceedings in Theoretical Computer Science 297, pp. 206–220.
Published: 19th July 2019.

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