In logic, an argumentum e contrario (Latin: 'argument from the contrary'; also a contrario or ex contrario[1]), also known as appeal from the contrary, denotes any proposition that is argued to be correct because it is not disproven by a certain case.
When analogy is allowed, e contrario is forbidden and vice versa.
[citation needed] Arguments e contrario are often used in the legal system as a way to solve problems not currently covered by a certain system of laws.
In law, the use of the argumentum e contrario finds its footing in the Latin maxim: ubicumque lex voluit dixit, ubi tacuit noluit that runs as follows: If the Legislator wished to say something, he would do that expressly.
On the other hand, this example: Novel legal cases often hinge on more cogent arguments of the form: