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Informal fallacies are a type of incorrect argument in natural language. The source of the error is not just due to the form of the argument, as is the case for formal fallacies, but can also be due to their content and context. Fallacies, despite being incorrect, usually appear to be correct and thereby can seduce people into accepting and using them. These misleading appearances are often connected to various aspects of natural language, such as ambiguous or vague expressions, or the assumption of implicit premises instead of making them explicit.
Traditionally, a great number of informal fallacies have been identified, including the fallacy of equivocation, the fallacy of amphiboly, the fallacies of composition and division, the false dilemma, the fallacy of begging the question, the ad hominem fallacy and the appeal to ignorance. There is no general agreement as to how the various fallacies are to be grouped into categories. One approach sometimes found in the literature is to distinguish between fallacies of ambiguity, which have their root in ambiguous or vague language, fallacies of presumption, which involve false or unjustified premises, and fallacies of relevance, in which the premises are not relevant to the conclusion despite appearances otherwise.
Some approaches in contemporary philosophy consider additional factors besides content and context. As a result, some arguments traditionally viewed as informal fallacies are not considered fallacious from their perspective, or at least not in all cases. One such framework proposed is the dialogical approach, which conceives arguments as moves in a dialogue-game aimed at rationally persuading the other person. This game is governed by various rules. Fallacies are defined as violations of the dialogue rules impeding the progress of the dialogue. The epistemic approach constitutes another framework. Its core idea is that arguments play an epistemic role: they aim to expand our knowledge by providing a bridge from already justified beliefs to not yet justified beliefs. Fallacies are arguments that fall short of this goal by breaking a rule of epistemic justification. A particular form of the epistemic framework is the Bayesian approach, where the epistemic norms are given by the laws of probability, which our degrees of belief should track.
The study of fallacies aims at providing an account for evaluating and criticizing arguments. This involves both a descriptive account of what constitutes an argument and a normative account of which arguments are good or bad.[1][2] In philosophy, fallacies are usually seen as a form of bad argument and are discussed as such in this article. Another conception, more common in non-scholarly discourse, sees fallacies not as arguments but rather as false yet popular beliefs.[3]