Donkey Brain!

Denying or Negating the Antecedent is a formal fallacy that has the following argumentative structure:

1. If P, then Q.
2. Not P.
3. Therefore, not Q

This fallacy is often confused for the valid argument Modus Tollens which has the following structure:

1. If P, Then Q.
2. Not Q.
3. Therefore, not P. 

The comedy show It's Always Sunny in Philadelphia presents an excellent example of Denying or Negating the Antecedent in the following clip:

If we reconstruct the argument it goes:

1. If one has donkey brains, then they make foolish decisions.
2. Frank does not have a donkey brain.
3. Therefore, he does not make foolish decisions.