Argumentum a contrario

In logic, an argumentum a contrario (Latin: "appeal from the contrary" or "argument based on the contrary") denotes any proposition that is argued to be correct because it is not disproven by a certain case. It is the opposite of the analogy. Arguments a contrario are often used in the legal system as a way to solve problems not currently covered by a certain system of laws. Although it might be used as a logical fallacy, arguments a contrario are not by definition fallacies.