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Affirming the consequent
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==Additional examples== {{unreferenced section|date=December 2023}} '''Example 1''' One way to demonstrate the invalidity of this argument form is with a counterexample with true premises but an obviously false conclusion. For example: :If someone lives in [[San Diego]], then they live in [[California]]. :Joe lives in California. :Therefore, Joe lives in San Diego. There are many places to live in California other than San Diego. On the other hand, one can affirm with certainty that "if someone does not live in California" (''non-Q''), then "this person does not live in San Diego" (''non-P''). This is the [[contrapositive]] of the first statement, and it must be true if and only if the original statement is true. '''Example 2''' :If an animal is a dog, then it has four legs. :My cat has four legs. :Therefore, my cat is a dog. Here, it is immediately intuitive that any number of other antecedents ("If an animal is a deer...", "If an animal is an elephant...", "If an animal is a moose...", ''etc.'') can give rise to the consequent ("then it has four legs"), and that it is preposterous to suppose that having four legs ''must'' imply that the animal is a dog and nothing else. This is useful as a teaching example since most people can immediately recognize that the conclusion reached must be wrong (intuitively, a cat cannot be a dog), and that the method by which it was reached must therefore be fallacious. This argument was featured in [[Rhinoceros (play)|Euguene Ionesco's Rhinoceros]] in a conversation between a Logician and an Old Gentleman. '''Example 3''' In ''[[Catch-22]]'',<ref name=":0">{{Cite book|title=Catch-22|last=Heller|first=Joseph|publisher=Vintage|year=1994|isbn=0-09-947731-9|pages=438, 8}}</ref> the chaplain is interrogated for supposedly being "Washington Irving"/"Irving Washington", who has been blocking out large portions of soldiers' letters home. The colonel has found such a letter, but with the chaplain's name signed. :"You can read, though, can't you?" the colonel persevered sarcastically. "The author signed his name." :"That's my name there." :"Then you wrote it. [[Q.E.D.]]" ''P'' in this case is 'The chaplain signs his own name', and ''Q'' 'The chaplain's name is written'. The chaplain's name may be written, but he did not necessarily write it, as the colonel falsely concludes.''<ref name=":0" />
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