Affirming the consequent:

Formal Fallacy
Definition Example
When the antecedent in a conditional is claimed to be true because the consequent is true; if A, then B; B, therefore A. Whenever it rains, people carry umbrellas. People are carrying umbrellas, so it must be raining.
  Notes
The form of this fallacy is as follows.

If P, then Q
Q
Therefore, P

This is a formal fallacy that is always fallacious.


Case Study One

“If God answers prayer, then it is raining outside. It is raining outside. Therefore, God answers prayer.*


Case Study Two

“If I am a husband, I am married. I’m married. Therefore, I’m a husband.”
(No, you could be a wife.)


Case Study Three

“If someone is psychic, they can predict stock prices. My broker predicts stock prices. Therefore, he is psychic.”


Keep in mind that a fallacious argument does not entail an erroneous position.


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