Formal Fallacy: Affirming the consequent

Affirming the Consequent is a formal fallacy to do with the validity of the form of the argument and not the meaning or misunderstanding of language. The pattern of the argument is the issue. This is a type of Modus Ponens argument (Latin: the way that affirms by affirming).

If p then q

q
Therefore, p.

Examples:

If Rommel was killed in a plane crash, then Rommel is dead.  (If p -> q)

Rommel is dead (p)
Therefore , Rommel was killed in a plane crash. (q)

If I Am in Minneapolis, then I am in Minnesota.

I am in Minnesota.
Therefore, I am in Minneapolis

If the mill were polluting the river, then we would see an increase in fish deaths.

And fish deaths have increased.
Thus, the mill is polluting the river.

Proof: This shows that even though the premises are true, the conclusion could be false. The fish deaths can be caused by something else and not the mill. It could have been pesticide run-off or something else?

Rommel is dead, but he did not die in a plane crash.

I don’t have to be in Minneapolis, I can be in St. Paul.


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