Contradiction

We know that a preposition cannot be both true and false.

There will never be a situation where the statement above is true.

Recognizing a contradiction may require a little sleuthing on your part, particularly if someone with a motive is trying to insist that there is no contradiction. That person most likely won’t say a statement and then repeat it again with a “no” or “not” in it somewhere to negate it.

(See also Tautology)