fallacy, in logic, a term used to characterize an invalid argument. Strictly speaking, it refers only to the transition from a set of premises to a conclusion, and is distinguished from falsity, a value attributed to a single statement. The laws of syllogisms were systematically elaborated by Aristotle, and for an argument to be valid, it must adhere to all the laws to be fallacious, it need only break one (see syllogism ). The term fallacy has come to be used in a somewhat wider sense than the purely formal one. Informal fallacies are said to occur when statements are ambiguous or vague as to the logical form they represent, or when a multiplicity of meaning is present and the validity of the argument depends on switching meanings of a word or a phrase in midstream.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

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