Casuistry was practiced widely during the Middle Ages and the Renaissance to resolve moral issues. Although casuistry largely fell silent during the modern period, in The Abuse of Casuistry: A History of Moral Reasoning (1988), Toulmin collaborated with Albert R. Jonsen to demonstrate the effectiveness of casuistry in practical argumentation during the Middle Ages and the Renaissance, effectively reviving it as a permissible method of argument.
Casuistry employs absolutist principles, called "type cases" or "paradigm cases," without resorting to absolutism. It uses the standard principles (for example, sanctity of life) as referential markers in moral arguments. An individual case is then compared and contrasted with the type case. Given an individual case that is completely identical to the type case, moral judgments can be made immediately using the standard moral principles advocated in the type case. If the individual case differs from the type case, the differences will be critically assessed in order to arrive at a rational claim.
Through the procedure of casuistry, Toulmin and Jonsen identified three problematic situations in moral reasoning: first, the type case fits the individual case only ambiguously; second, two type cases apply to the same individual case in conflicting ways; third, an unprecedented individual case occurs, which cannot be compared or contrasted to any type case. Through the use of casuistry, Toulmin demonstrated and reinforced his previous emphasis on the significance of comparison to moral arguments, a significance not addressed in theories of absolutism.