Input/output logics

In a range of contexts, one comes across processes resembling inference, bu t where input propositions are not in general included among outputs, and t he operations is not in any way reversible. Examples arise in contexts of c onditional obligations, goals, ideals, preferences, actions, and beliefs. O ur purpose is to develop a theory of such input/output operations. Four are singled out: simple-minded, basic (making intelligent use of disjunctive i nputs), simple-minded reusable (in which outputs may be recycled as inputs) and basic reusable. They are defined semantically and characterised by der ivation rules, as well as in terms of relabeling procedures and modal opera tors. Their behaviour is studies on both semantic and syntactic levels.