Consider the argument:
If p, then q.
If God had wanted us to fly, He would |
have given us wings.
He has not given us wings.
Therefore, He did not want us to fly.|
If we assume that q is false, we can infer that p is false--for
if p were not false (i.e., if it were true), then q could not
have been false either.
In this case, we denied the consequent, and that allowed
us to deny the antecedent. Once again, the conclusion is a