What is Input/Output Logic? Input/Output Logic, Constraints, Permissions

We explain the {em raison d\u27^etre} and basic ideas of input/output logic, sketching the central elements with pointers to other publications for detailed developments. The motivation comes from the logic of norms. Unconstrained input/output operations are straightforward to define, with relatively simple behaviour, but ignore the subtleties of contrary-to-duty norms. To deal with these more sensitively, we constrain input/output operations by means of consistency conditions, expressed via the concept of an outfamily. They also provide a convenient platform for distinguishing and analysing several different kinds of permission