Fallacies

Errors with staying power. To be a fallacy, someone must fall for it, as Lewis Carroll points out,

Any argument which deceives us, by seeming to prove what it does not really prove, may be called a ‘Fallacy’ (derived from the Latin verb fallo “I deceive”).^F1

Both formal and informal logic recognise the existence of fallacies. From the point of view of formal logic, a fallacy is an error which violates the laws of reasoning; it can be demonstrated as an error in many ways—with the use of (for instance) symbols, diagrams, words, maths, computer syntax. These, in the terms of formal logic, are “genuine fallacies”.

Informal logic, on the other hand, recognises many other kinds of fallacies; a number do indeed violate the laws of reasoning (like Begging the Question), but others are more about the equivocal use of language (Devil’s Voice), or humour (Play), or submission to a threat (Big Stick), or distraction (Contrarian Fallacy), or a misconception about the way systems work (Death), or long-held errors about matters of fact (Ignorance). For a whistle-stop tour of such informal fallacies, see “How To Cheat in an Argument”).^F2

Informal fallacies can be used for good purposes or bad, but the risk of their causing trouble—especially for those unfamiliar with them—is significant. Studying them helps develop the art of coherent argument, as well as improving awareness of its importance, and assists the diagnosis when a dialogue goes wrong. It may also suggest a cure.^F3

Related entries:

Manners, Deceptions.