Tag Archives: ad hoc

Ad hoc fallacy

In July 2009, Danish psychic/dowser Connie Sonne was given the chance to prove her claimed dowsing ability in the One Million Dollar Paranormal Challenge offered by the James Randi Educational Foundation. She was asked to dowse some randomly selected cards hidden in envelopes and lost the challenge by selecting other incorrect ones. In an interview afterward, she insisted that she lost merely because, “…it wasn’t time yet for my powers to be revealed.”

The ad hoc fallacy is not strictly an error of logic. Instead, it a fallacious rhetorical tactic in which a person presents a new explanation that is unjustified or simply unreasonable, in an attempt to rescue their original claim after evidence that contradicts it has emerged.

The Latin phrase “ad hoc” is literally translated as meaning “to this”. It refers to an idea or solution that is intended for a specific use, and not for any other uses. An ad hoc explanation is specifically constructed to be used in a particular case and is created hastily at the moment rather than being the result of deliberate, fact-based reasoning.

Another example encountered by skeptical investigators is as follows. This is a typical conversation between a supposed psychic who claims to be able to read minds and a skeptic.

Skeptic: “If you’re psychic then tell me what number I am thinking of”                        

Psychic: “My powers don’t work in the presence of skeptics.”

In this example, the fallacious tactic is pretty obvious. The response that their powers don’t work around skeptics is clearly a ridiculous explanation, and it’s an explanation that one would never accept unless one was already convinced that the person was a psychic. Further, it makes it impossible to discredit them no matter how fraudulent they actually are (a lack of falsifiability is a hallmark of ad hoc fallacies).

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No true Scotsman

No true Scotsman is a kind of informal fallacy in which one attempts to rescue a universal generalisation from counterexamples by changing the definition in an ad hoc fashion to exclude the counterexample. Rather than denying the counterexample or rejecting the original claim, this fallacy modifies the subject of the assertion to exclude the specific case or others like it by rhetoric i.e. those who perform that action are not part of our group and thus criticism of that action is not criticism of the group.

Philosophy professor Bradley Dowden explains the fallacy as an ‘ad hoc rescue’ of a refuted generalisation attempt. The following is a simplified rendition of the fallacy:

Person A: ‘No Scotsman puts sugar on his porridge.’

Person B: ‘But my uncle Angus likes sugar with his porridge.’

Person A: ‘Ah yes, but no true Scotsman puts sugar on his porridge.’

The introduction of the term is attributed to British philosopher Prof. Antony Flew, because the term originally appeared in Flew’s 1971 book An Introduction to Western Philosophy.

A practical example of this fallacy occurs when Marxists try to defend their regressive and unworkable ideology against the overwhelming evidence from the 20th century that almost every communist regime was brutally repressive; and most of them resulted in poverty for everybody except the communist party elite. ‘But they weren’t true communists’ they say. Yeah, right.

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