A fallacious argument can still land on a true conclusion
Faulty reasoning does not guarantee a false answer. Affirming the consequent is a textbook error, yet it can stumble onto the truth by accident. What makes an argument fallacious is that its conclusion fails to follow, whatever the conclusion happens to be. Aristotle was the first to catalogue such traps systematically.
Aristotle, who lived from 384 to 322 BC, listed thirteen fallacies in his Sophistical Refutations, splitting them into those that depend on language and those that do not. His aim was partly practical: knowing the errors made it easier to refute an opponent and win a debate. Indian logicians worked just as hard. The Nyāya Sūtras, attributed to Aksapada Gautama and dated anywhere from the 6th century BCE to the 2nd century CE, identified faulty reasons such as one that proves the opposite of what it claims, as in arguing that sound is eternal because it is produced.
Modern logic separates formal fallacies from informal ones. A formal fallacy, also called a non sequitur, meaning it does not follow, is a structural flaw that makes a deductive argument invalid regardless of whether its premises are true. An informal fallacy lies in the content instead, so an argument can be formally valid and still unpersuasive. Hasty generalisation, drawing sweeping claims from a sample too small or unusual, is a common informal kind, and stereotypes are everyday examples.
Classification has always varied. Richard Whately, an English theologian of the early 19th century, split fallacies into logical and material types. Francis Bacon grouped the mind's typical errors into four Idols, J. S. Mill discussed them in his Logic, and Jeremy Bentham wrote a Book of Fallacies. Pragma-dialectical theory treats a fallacy as a broken rule in a conversation aimed at settling a disagreement.
Spotting fallacies in real life is harder than in textbooks. Arguments come wrapped in rhetoric, may mix sound and faulty stages, and often appeal to emotion. Maarten Boudry and others argue that strictly deductive fallacies rarely occur, because once context and prior probabilities are considered, many supposedly fallacious moves become reasonable inductive guesses. Propaganda, advertising and opinion-driven media still supply plenty of genuine specimens.
Source: Fallacy
