Fallacy

Fallacy is a term used in logic to describe an argument that uses poor reasoning. An argument can be fallacious whether or not its conclusion is true. Fallacies can be categorized into formal fallacies and informal fallacies.

Formal Fallacies

A formal fallacy is a pattern of reasoning that is always wrong. This is due to a flaw in the logical structure of the argument which renders the argument invalid. A formal fallacy is contrasted with an informal fallacy, which may have a valid logical form and yet be unsound because one or more premises are false.

Informal Fallacies

Informal fallacies – arguments that are fallacious for reasons other than structural (formal) flaws and usually require examination of the argument's content. Informal fallacies can be categorized into three types: fallacies of relevance, fallacies of weak induction, and fallacies of presumption, ambiguity, and illicit transference.

Fallacies of Relevance

These fallacies appeal to evidence or examples that are not relevant to the argument at hand.

• Ad Hominem – attacking the person making the argument, rather than the argument itself, when the attack on the person is completely irrelevant to the argument the person is making.
• Appeal to Authority – where an assertion is deemed true because of the position or authority of the person asserting it.

Fallacies of Weak Induction

These fallacies occur when the premises are not strong enough to support the conclusion.

• Hasty Generalization – basing a broad conclusion on a small or unrepresentative sample.
• Post Hoc – reasoning that because two events occurred in succession, the former event caused the latter event.

Fallacies of Presumption, Ambiguity, and Illicit Transference

These fallacies occur due to ambiguity in language or meaning.

• Begging the Question – a circular argument, in which the conclusion is included in the premise.
• Equivocation – using a word in a different way than the author intended.

See Also

• List of fallacies
• Cognitive bias
• Propaganda techniques

References

Fallacy Resources
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