A fallacy is an incorrect argument. A fallacy may be incorrect in:
- deriving a conclusion which does not necessarily follow from the hypotheses;
- inadequately explaining the conclusion's relation to the hypotheses, even if it does follow from them;
- coming to a dumbass conclusion.
Fallacies and cultures
Different cultures take different stances towards fallacies: some abhor them, some are indifferent, and some are actually based on them (see modern-day USA).
In Ancient Greece, they were considered social faux-pas, and the perpetrators, besides not being invited to parties, earned all sorts of nicknames, from "doody-head" to "sophist." (Which is the origin of the term "sophisticated" — someone who, through logical fallacies, got fooled into thinking that paying US$5,000 for a US$50 piece of clothing is something to brag about.)
Twenty-first century Brazil is a good example of indifference to fallacies. The average Brazilian, when considering an argument, is primarily interested in whether the conclusion agrees with what he or she already thinks. If it doesn't, they reject it immediately, unless it shows some promise of getting them on TV. Brazilians, though warm and hospitable, are angered when confronted about this, usually saying "that's not what I think at all."
Philosophy of fallacies
Most philosophers reject the fallacies that they can spot.
Nevertheless, one philosophical school, founded in the early twentieth century mainly by dumb people, protested that there is circularity in using logic to ascertain what is a correct argument, and at the same time using correct arguments as the basis for logic. They thus maintained that logic itself is a fallacy. However, as Gödel argued, the notion of fallacy depends on logic, and therefore not only is the concept of fallacy fallacious, but the entire preceding discussion as well. He concludes that, since the discussion had proved itself fallacious, and was fallacious, then it must be true, and so people may carry on as before.
The aftermath of this dispute involved much head-scratching, and dozens of philosophers voluntarily joining the ranks of dumb people. Since then most humanities majors have consistently avoided logic and its vicinities.
One of the most widespread fallacies has the formal name of modus ponens. From two premises, of the form and , it attempts to deduce . For example, by the modus ponens fallacy, from the true propositions "the letter A shot the letter B with an arrow" and "the letter A" you would be able to deduce the incorrect proposition "the letter B".
An important open problem in logic is to find out what exactly people mean when they say "the letter B". Leading logicians such as Dwight D. Eisenhower hope to solve it by building on previous results on "the letter A", which is now considered to be well understood.
Other common fallacies include:
- Phallusy fallacy: An argumentative fallacy in which one person bases his or her argument on the size of his or her penis.
- Reductio ad absurdum: An argumentative fallacy in which, desperate to win the argument, one person flicks his magic wand and casts the spell of the same name, shrinking his opponent down to an absurd size.
- No true Scotsman fallacy: The mistake made by someone who tries to critique selectively chosen definitions instead of meeting leading questions based on them. Scientists are always committing this fallacy. You'll prove them wrong based on the fact that carbon weighs 12 atomic units, and they'll be like, I'm talking about carbon-14. Excuse me, scientists, carbon-14?? I'm pretty sure there's only one kind of carbon.
- Fallacy of leading questions: This is when someone asks, "Have you stopped beating your wife?" This frequent example of the fallacy is literally the only one there is.
- Fallacy of sensitivity: Allows you to avoid addressing an alternative case, because it is a really taboo subject. For example:
"Critics allege that certain parts of the USA's foreign policy have been questionable. Since America would never put the lives of foreigners at risk (this is the use of the fallacy of sensitivity), this cannot be true."
- Reductio ad Hitlerum: Do you know who else used this fallacy...?
- Argumentum ad baculum: In which one person attempts to gain points by claiming that actor Scott Bakula, were he present, would totally agree with him or her.
- Pathetic fallacy: Sucks.
- Texas sharpshooter fallacy: Pretty much what you'd expect. Generally fatal.
- Fallacy of exclusive premises: In which one person urges the other to get the hell off his land.
- Circular reasoning: Is a kick-awesome way to prove anything from anything. Most programming languages provide it as the concept of recursive functions.
- The fundamental fallacy: The idea that human intellect is a simplistic phenomenon whose misconceptions can be analyzed categorically into a small number of fallacies.