A system and method are provided for specifying a legality expression for use in a system for processing the legality expression. The system and method include providing a legality expression language, including at least one of a duty element specifying an obligation that a principal must perform an act, a ban element specifying a prohibition that a principal must not perform an act, an intent element specifying an intention that a principal wants to perform an act, and a claim element specifying an assertion that a principal does perform an act. The system and method further include interpreting by the system a legality expression specified using the legality expression language.