Institute for Mathematical Behavioral Sciences

The norms of good and bad faith are informal ones but also arise in legal usage. Because they are specific to a context such as negotiations and contracts, and are hard to define even then, many writers have doubted that they have any clear, broad, meaning. This paper proposes that acting in bad faith is having a duty to another and communicating to them one is doing that, when in fact one does not believe that is so. Good faith is doing the same, but doing it sincerely. Since the concept of communication used here does not require explicit language, bad faith is more general than lying. An axiomatic theory of communication shows how bad faith arises in various speech acts including assertions, promises, requests and offers. The analysis has implications especially for apologies, explaining why the recipient often wants to hear an explicit "I apologize" and often sees a particular apology as unsatisfactory.