The paradoxes of deontic logic revisited: a computer science perspective

This paper revisits a number of well-known paradoxes of deontic logic, namely Ross'paradox (if you ought to mail a letter, you ought to mail or burn it), the free choice paradox (if you are permitted to mail a letter, you are permitted to mail or burn it), the paradox of No Conflicting Obligations (ought implies permitted), the Good Samaritan Paradox (if you ought to help Jones who is robbed, then Jones ought to be robbed) and Chisholm's paradox (if you ought to do A, and if A ought to imply B, and not A implies that you ought to do not B, then this is inconsistent with doing not A). Framing these paradoxes in dynamic logic removes some of them and sheds light on others. This paper is based on an invited talk presented at DEON'94