n. 1. the logical study of such concepts as possibility, necessity, contingency, etc., and of formal systems of which the intended interpretation includes such concepts. 2. the study of analogous families of concepts, such as moral, epistemological and psychological concepts, and of systems intended to represent them. See alethic logic, deontic logic, epistemic logic, doxastic logic. 3. any formal system capable of being interpreted as a model for the behaviour of such concepts.