Affirming the Consequent / Denying the Antecedent

[aion]

Affirming the consequent. This is the most basic fallacy of logic. The essence of it I can explain with a simple example. It is perfectly valid to argue from the truth of propositions to the truth of conclusions in the following way. Take as true a premise such as Aristotle is a man; add to it a true proposition such as all men eat tomatoes; to reach a valid conclusion like: Aristotle eats tomatoes. Affirming the consequent argues backward from the truth of a conclusion to the truth of one of the propositions like this. Gustav eats tomatoes. All men eat tomatoes. Therefore, Gustav is a man, when in fact Gustav is the Dachshund who raids ripe tomatoes near the ground.

http://www.kilty.com/reason.htm

http://www.fallacyfiles.org/afthecon.html

http://www.fallacyfiles.org/denyante.html