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.
edit 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$ 5000 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. The brazilian folk, though warm and hospitable, are angered when confronted about this, usually saying "that's not what I think at all".
edit 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 the young 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. This became known as The Most Amazing Coincidence in logic.
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.
edit Common Fallacies
One of the most widespread fallacies is known by the 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.
ad homomen: An argumentative fallacy in which one person bases his argument on the premise that his opponent is gay.
Note: the above "fallacy" is in the wrong page and should be moved to Flawless Argumentative Masterstrokes
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 a manageable size.
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.
Joint effect: "Hey, man, you know, maybe we're all, like, the same person, y'know? So, when I'm arguing with you, it's totally like, like I'm arguing with myself. You know?"
Fallacy of exclusive premises: In which one person urges the other to get the hell off his land.
Super-sequitur: An argument that makes so much sense that it must be false. "This text is text." Said text is probably Captain Crunch.
Heresy fallacy: If I don't agree with it, it's wrong.