Mental reservation (or mental equivocation) is an ethical theory and a doctrine in moral theology which recognizes the "lie of necessity", and holds that when there is a conflict between justice and telling the truth, it is justice that should prevail. The doctrine is a special branch of casuistry (case-based reasoning) developed in the late Middle Ages and the Renaissance. While associated with the Jesuits, it did not originate with them. It is a theory debated by moral theologians, but not part of Canon law.