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For specific popular misconceptions, see List of common misconceptions.

A fallacy is incorrect argument in logic and rhetoric resulting in a lack of validity, or more generally, a lack of soundness. Fallacies are either formal fallacies or informal fallacies.

Contents

1 Formal fallacies 1.1 Propositional fallacies 1.2 Quantification fallacies 1.3 Formal syllogistic fallacies 2 Informal fallacies 2.1 Faulty generalizations 2.2 Red herring fallacies 3 Conditional or questionable fallacies 4 See also 5 References 6 Further reading 7 External links

Formal fallacies

Main article: Formal fallacy

A formal fallacy is an error in logic that can be seen in the argument's form.[1] All formal fallacies are specific types of non sequiturs.

Appeal to probability – takes something for granted because it would probably be the case (or might be the case).[2][3] Argument from fallacy – assumes that if an argument for some conclusion is fallacious, then the conclusion itself is false.[4] Base rate fallacy – making a probability judgement based on conditional probabilities, without taking into account the effect of prior probabilities.[5] Conjunction fallacy – assumption that an outcome simultaneously satisfying multiple conditions is more probable than an outcome satisfying a single one of them.[6] Masked man fallacy (illicit substitution of identicals) – the substitution of identical designators in a true statement can lead to a false one.[7]

Propositional fallacies

A propositional fallacy is an error in logic that concerns compound propositions. For a compound proposition to be true, the truth values of its constituent parts must satisfy the relevant logical connectives which occur in it (most commonly: , , , , ). The following fallacies involve inferences whose correctness is not guaranteed by the behavior of those logical connectives, and hence, which are not logically guaranteed to yield true conclusions.

Types of Propositional fallacies:

Affirming a disjunct – concluded that one disjunct of a logical disjunction must be false because the other disjunct is true; A or B; A; therefore not B.[8] Affirming the consequent – the antecedent in an indicative conditional is claimed to be true because the consequent is true; if A, then B; B, therefore A.[8] Denying the antecedent – the consequent in an indicative conditional is claimed to be false because the antecedent is false; if A, then B; not A, therefore not B.[8]

Quantification fallacies

A quantification fallacy is an error in logic where the quantifiers of the premises are in contradiction to the quantifier of the conclusion.

Types of Quantification fallacies:

Existential fallacy – an argument has a universal premise and a particular conclusion.[9]

Formal syllogistic fallacies

Syllogistic fallacies – logical fallacies that occur in syllogisms.

Affirmative conclusion from a negative premise (illicit negative) – when a categorical syllogism has a positive conclusion, but at least one negative premise.[9] Fallacy of exclusive premises – a categorical syllogism that is invalid because both of its premises are negative.[9] Fallacy of four terms (quaternio terminorum) – a categorical syllogism that has four terms.[10] Illicit major – a categorical syllogism that is invalid because its major term is not distributed in the major premise but distributed in the conclusion.[9] Illicit minor – a categorical syllogism that is invalid because its minor term is not distributed in the minor premise but distributed in the conclusion.[9] Negative conclusion from affirmative premises (illicit affirmative) – when a categorical syllogism has a negative conclusion but affirmative premises. [9] Fallacy of the undistributed middle