A fallacy is a defective argument. It is an error in reasoning. As we shall see in Chapters 4 and 6, sometimes the defect is in the form or structure of a deductive argument. These are invalid arguments. They are known as formal fallacies. For example, the following argument commits the formal fallacy, denying the antecedent:

The form or structure of the argument can be represented by replacing statements with variables:

Because the argument form is invalid, it is possible for an argument of that form to have true premises and a false conclusion:

Here the problem is with the form of the argument. The problem is independent of the content of the arguments, that is, the claims about José, Belinda, Bill Gates, and wealth.