One man's modus ponens is another man's modus tollens.

Modus tollens (Latin for *method of removing*) is a method of propositional logic of the form (where *P *and *Q *are logical propositions)

P implies Q.

Q is false.

Therefore, P is false.

For example: *If it is a car, it has wheels. It does not have wheels. Therefore, it is not a car*.

It's important not to* *make the converse error, which would be: *If it is a car, it has wheels. It has wheels. Therefore, it is a car. (not true, it could be a bus).*

There's also *modus ponens (method of putting), *which is a more intuitive method of interface of the form:

P implies Q.P is true.Therefore, Q is true.