History Main / ConverseError

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Has nothing to do with shoes (despite what Tropers/TheAdvertisementServer thinks).

!!'''[[http://en.wikipedia.org/wiki/Affirming_the_consequent Affirming the consequent]]''':

:: This claim is most simply put as:

-->If A, then B.\\
B.\\
Therefore, A.

:: It's a fallacy because at no point is it shown that A is the ''only'' possible cause of B; therefore, even if B is true, A can still be false. For example:

-->If my car was Ferrari, it would be able to travel at over a hundred miles per hour.\\
I clocked my car at 121 miles per hour.\\
Therefore, my car is a Ferrari.\\

:: This is popular in conspiracy theories. Here the fallacy is fairly obvious; given the evidence, the car ''might'' be a Ferrari, but it might also be a Bugatti, Lamborghini, or any other model of performance car, since the ability to travel that fast is not unique to Ferraris. Hell, it might even be a Subaru Outback. Note that while this may appear to call all hypothesis / evidence experiments fallacious, they are based on additional evaluations of the likelihood of ''other'' theories, thus establishing that A ''is'' a likely cause of B.

!!'''[[http://en.wikipedia.org/wiki/Denying_the_antecedent Denying the antecedent]]''':

:: The flip side of the above, where you say that because the initial conditions did not happen, the result is impossible.

--> If a person is wearing a hat, they have a head.\\
I am not wearing a hat.\\
Therefore I do not have a head.

:: Note that, by the [[http://en.wikipedia.org/wiki/Contrapositive contrapositive]] rule, these two fallacies are equivalent. For example, you could replace "If a person is wearing a hat, they have a head" by the logically identical statement "If a person has no head, they aren't wearing a hat" to turn the first example of denying the antecedent into an example of affirming the consequent.

!!!Examples:

[[foldercontrol]]

[[folder: Film ]]

* ''Film/MontyPythonAndTheHolyGrail'':
** On the soundtrack album, a logician sorting out the witch burning scene goes off on a tangent, stating that "given the premise 'all fish live underwater' and 'all mackerel are fish,' my wife concludes not that all mackerel live underwater but that [[InsaneTrollLogic if she buys kippers it will not rain, or that trout live in trees, or even that I do not love her anymore]]."
** The witch-burning scene is itself an extended example of Converse Error, of course - with the punchline being that they somehow land on the correct answer anyway. Their reasoning runs:
--> Ducks float.\\
This woman shares a notable quality (weight) with a duck.\\
Therefore, this woman must float.\\
Wood floats.\\
Therefore, this floating woman must be made of wood.\\
Things made from wood burn.\\
Witches burn.\\
Therefore, this woman made of wood must be a witch!

[[/folder]]

[[folder: Live Action TV ]]

* In ''Series/YesPrimeMinister'', Sir Humphrey Appleby explains the fallacy and how foolishly people can fall for it. He demonstrates the illogic of the fallacy by saying:
--> All cats have four legs.\\
My dog has four legs.\\
Therefore my dog is a cat!

[[/folder]]

[[folder: Western Animation ]]

* In ''WesternAnimation/AmericanDad'', Stan sinks his entire savings to build a rocket for Steve to win a contest.
-->'''Stan''': You gotta spend money to make money.\\
'''Francine''': But you didn't make any money!\\
'''Stan''': So logically, I didn't spend any money! [[NoFourthWall *waves at the camera*]] Goodnight everybody!

[[/folder]]

!! Looks like this fallacy but is not:
* Inference to the best explanation. The usual form of scientific reasoning, as well as a lot of Sherlock Holmes' "deductions" (though he's wrong to call them that, since this is a form of ''inductive'' reasoning).
-->B.\\
The best explanation for B would be A.\\
Therefore, A (probably).
** This differs from the Ferrari example above in that it posits a stronger connection between A and B than just A's truth entailing B's; B is actually giving some positive reason to ''prefer'' A over the other possibilities. Also, this form of argument isn't claiming deductive certainty, so the bar is a little lower for it being acceptable.
*** An example to compare with the Ferrari one above would be: I clocked my car at 121 mph, therefore it is likely to be a high-performance car (i.e. Ferrari, Bugatti, Lamborghini, etc...) rather than an average family car.
** Scientific reasoning is frequently attacked by those who understand this fallacy, but not the scientific method, which has the following form:
--> B.\\
A is the best explanation for B, so I will claim "A is the most likely explanation."\\
If A, then C.\\
Therefore, if not C, not A (valid contrapositive).\\
Is C true? Yes? I will increase my confidence that A is the correct explanation.\\
If A, then D.\\
Not D!\\
I must provisionally reject A or modify it to account for D, then continue to seek new information and propose new possible explanations.
----

[[/folder]]

[[AC:{{Film}}]]

[[AC:LiveActionTV]]

[[AC:WesternAnimation]]

** The witch-burning scene is itself an extended example of ConverseError, of course - with the punchline being that they somehow land on the correct answer anyway. Their reasoning runs: