Fallacy

Fallacy, the incorrect performance of the process of reasoning so as to lead to error. The science of Logic reduces sound reasoning to certain rules, and when any of these rules is violated a logical fallacy is the result. The time-honoured division was into two classes, according as the error lay in the form of the reasoning or in the matter: the formal were entitled in dictione, or those appearing in the expression; the material were entitled extra dictionem, implying that the fault could not be detected from the language, but must be sought in a consideration of the meaning or subject-matter. Mill proposed to classify all fallacies under (1) Fallacies of Simple Inspection, or Fallacies a priori, which includes the whole of what may be termed Natural Prejudices; (2) Fallacies of Observation; (3) Fallacies of Generalisation, including Induction; (4) Fallacies of Ratiocination or Syllogism; and (5) Fallacies of Confusion, comprehending the petitio principii, the ignoratio elenchi, and ambiguous language generally. Other classifications have been more or less elaborately carried out. But, owing to the enormous variety and intricacy of inaccurate and confused modes of thought, it is difficult to draw up a scheme at once complete and rigorously scientific. See the articles LOGIC, INDUCTION, SYLLOGISM; for Bacon's eidōla, prejudices influencing the judgment, see BACON; and for the subject of fallacies generally, see the text-books of logic, as those of Whately, Mill, Jevons, and Fowler.