User:Bob K31416/F

"Aristotle's distinction between fallacies in dictione and fallacies extra dictionem is not the same as [Richard] Whately's division into logical, and non-logical or material. By "logical" fallacies Whately meant those in which "the conclusion does not follow" from the premisses; by "material," those in which the "conclusion does follow" from the premisses. In the former class, the defect of proof lies either in a manifest violation of some of the formal laws of the syllogism--quaternio terminorum, undistributed middle, illicit major, illicit minor, negative premisses, etc., defects which remain even when symbols are substituted for the terms and concepts, and which Aristotle would not regard as sophisms owing to the transparency of the mistake;--or the defect lies in a similar violation masked in ambiguous language. The transparent defects Whately called purely logical, the cloaked defects semi-logical fallacies. The latter he regarded as all alike reducible to ambiguous middle term, including in this class all Aristotle's sophisms except the ignoratio elenchi, the petitio principii, and the non causa pro causa. These three he included in his "material" fallacies, by which he understood mistakes due to assuming false or unproven premisses, or premisses which prove the wrong conclusion. Whately's main distinction--between formally inconclusive arguments, and other sources of error--is sound and intelligible. But his nomenclature is objectionable. It is due to his narrow, nominalistic view of the scope of logic. All fallacies are logical, inasmuch as they are violations of logical principles or canons. Then, although most of Aristotle's sophismata, included in Whately's class of "semi-logical" fallacies, do in fact usually lead to formally invalid syllogisms through ambiguous middle terms, yet this is not clear in regard to some; and they certainly may lead to error otherwise as well. Hence the attempt to group them under such a head is unsatisfactory. Finally, on his own view of the scope of logic, Whately should not have dealt at all with what he called "non-logical" or "material" fallacies. The distinction between a "formal" fallacy and a "material" fallacy is not fixed or clear--any more than that between "formal" and "material" logic. But at all events in a reasoning process, we can distinguish between the narrower "formal" or "consistency" aspect, which is independent of the truth of the premisses and the meaning of the terms used, and the "material" or "truth" aspect. Now, the formal validity of an inference, in this narrow sense, being independent of the subject-matter, i.e. of the meaning of the concepts and terms employed, it is only when the invalidity persists with the symbols, i.e. when some of the formal laws of reasoning are violated, that the fallacy is a formal one. If the fallacy lies in the language, .i.e. in the meaning of the terms employed, in ambiguitites of meaning, then its source is in the subject-matter, in the things for which the terms stand, and the fallacy is a material fallacy. An ambiguous middle term in a syllogism is, therefore, in this sense a material fallacy: when its two distinct meanings are explicitly substituted for it by two distinct terms, we have immediately the formal fallacy of quaternio terminorum. In this meaning of the expression "material fallacy," all Aristotle's sophismata in dictione are, when they enter into an inference, material fallacies; while some of his fallacies extra dictionem are formal in the sense that they can be represented in sysmbols; so that it is a mistake to confound Aristotle's two lists with Whately's semi-logical and material fallacies, respectively: a mistake into which Jevons seems to have fallen."

- Peter Coffey


 * Whately's division into logical, and non-logical or material.
 * By "logical" fallacies Whately meant those in which "the conclusion does not follow" from the premisses
 * the defect of proof lies either in
 * a manifest violation of some of the formal laws of the syllogism--quaternio terminorum, undistributed middle, illicit major, illicit minor, negative premisses, etc., Called purely logical fallacies.
 * or in a similar violation masked in ambiguous language. Called semi-logical fallacies. — Includes all of Aristotle's sophisms except the ignoratio elenchi, the petitio principii, and the non causa pro causa.
 * by "material," those in which the "conclusion does follow" from the premisses.
 * Includes Aristotle's sophisms the ignoratio elenchi, the petitio principii, and the non causa pro causa.
 * Mistakes due to assuming false or unproven premisses, or premisses which prove the wrong conclusion.

Richard Whately's Fallacies
Richard Whately divided fallacies into two groups: logical and material. According to Whately, Logical fallacies are arguments where the conclusion does not follow from the premisses. Material fallacies are not logical errors because the conclusion does follow from the premisses. He then dived the logical group into two groups: purely logical and semi-logical. The semi-logical group included all of Aristotle's sophisms except:ignoratio elenchi, petitio principii, and non causa pro causa, because they where in the material group.