I came a cross this formal fallacie: If today is Saturday then tomorrow is Sunday. Is not Saturday. Tomorrow is no Sunday. I understand that the structure of the argument is not valid (denying the antecedent). But in this case to give this as an example is hard to absorb the idea that there trying to convinced you of( At least a think that) that this is a invalid form of an arguement. I would like to know your opinions. Thank you.