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A Fallacy is an error in reasoning that renders an argument invalid:

"A fallacious argument is a defective argument," says Michael F. Goodman, "and a fallacy is the defect in the argument itself. . . . Any argument committing one of the informal fallacies is an argument in which the conclusion does not follow conclusively from the premise(s)" (First Logic, 1993).

Observations on Fallacy

  • "In logic and the generalized study of reasoning, there are generally understood to be such things as good reasoning and bad reasoning. Typically, bad reasoning is characterized by falling into one or more of the classically compiled logical fallacies. A logical fallacy is simply a failure of logic. Arguments that are said to be fallacious have gaping holes or misleading leaps in their structure and reasoning."
    (J. Meany and K. Shuster, Art, Argument, and Advocacy. IDEA, 2002)
  • "An informal fallacy is an attempt at making a logical argument where there’s a failure in the reasoning itself. This can stem from a number of causes, such as the misapplication of words and phrases, or misunderstandings based on inappropriate assumptions. Illogical sequences in an argument can also cause informal fallacies. While informal fallacies can result in inaccurate arguments and false conclusions, that doesn’t mean they can’t be very persuasive."
    (Russ Alan Prince, "How To Bolster Your Negotiations With Informal Fallacies." Forbes, June 7, 2015)


"A fallacy is so conceived that if an argument exhibits a fallacy, it is probably a bad one, but if the argument exhibits no such violation, it is a good one.
"Fallacies are mistakes in reasoning that do not seem to be mistakes. Indeed, part of the etymology of the word 'fallacy' comes from the notion of deception. Fallacious arguments usually have the deceptive appearance of being good arguments. That perhaps explains why we are so often misled by them."
(T. Edward Damer, Attacking Faulty Reasoning, 2001)


"[O]ne clear sense of fallacy that we will encounter will involve a shift away from the correct direction in which an argumentative dialogue is progressing. By various means, an arguer may impede the other party from making her point or may attempt to draw the discussion off track. In fact, one popular modern approach to understanding fallacious reasoning is to see it as involving violations of rules that should govern disputes so as to ensure that they are well conducted and resolved. This approach, put forward by [Frans] van Eemeren and [Rob] Grootendorst in several works, goes by the name of 'pragma-dialectics.' Not only is each of the traditional fallacies understood as a violation of a discussion rule, but new fallacies emerge to correspond to other violations once we focus on this way of conducting arguments."
(Christopher W. Tindale, Fallacies and Argument Appraisal. Cambridge University Press, 2007)

Pronunciation: FAL-eh-see

Also Known As: logical fallacy, informal fallacy

From the Latin, "deceive"

From the Latin, "deceive"