Informally, this means that arguments of this form do not give good reason to establish their conclusions, even if their premises are true.
The only situation where one may deny the antecedent would be if the antecedent and consequent represent the same proposition, in which case the argument is trivially valid (and it would beg the question) under the logic of modus tollens.
One way to demonstrate the invalidity of this argument form is with an example that has true premises but an obviously false conclusion.
For example: That argument is intentionally bad, but arguments of the same form can sometimes seem superficially convincing, as in the following example offered by Alan Turing in the article "Computing Machinery and Intelligence": However, men could still be machines that do not follow a definite set of rules.
Another example is: [This is a case of the fallacy denying the antecedent as written because it matches the formal symbolic schema at beginning.