Rules and Exceptions, in Law and Elsewhere

The structure of rule systems in different domains is addressed. A rule system is viewed as a mechanism delivering certain outputs (the system’s conclusions) given certain external inputs, and certain internal structures and processes. It is specified what it means for a rule system to consist of rules and exceptions rather than of flat rules. It is argued that there are three main exception structures: inhibitory input links, inhibitory rules, and prioritized conflicting rules. These structures can be found in many rule systems, including the law, and international law in particular. They make it so that rule systems provide defeasible outputs in response to incoming signals, namely outputs that may no longer be provided when a larger input set is given. It is argued that the current jurisprudential debate on rules and exceptions (as well as the debate on defeasibility) needs to be lifted beyond the law for clarity to be achieved on the existence, genesis, and function of systems of rules and exceptions.