Deductive Fallacies

There are some forms or argument that look like deductions, but which are not. Here are the three most common invalid argument forms (or “deductive fallacies”) that are easily mistaken for deductions:

Undistributed Middle

In Aristotelian syllogisms, the middle term (the one that is present in both premises) must be distributed that is, is must be said to apply to all or to none of one of the other terms. The fallacy of undistributed middle is committed when one has an argument that looks like an Aristotelian syllogism, except that the middle term is not distributed. Here's are some examples:

Affirming the Consequent

Denying the Antecedent