Denying the antecedent is an invalid form of reasoning that is typically identified and frowned upon as a formal fallacy. Contrary to arguments that it does not or at least should not occur, denying the antecedent is a legitimate and effective strategy for undermining a position. Since it is not a valid form of argument, it cannot prove that the position is false. But it can provide inductive evidence that this position is probably false. In this role, it is neither (...) defective nor deceptive. Denying the antecedent provides inductive support for rejecting a claim as improbable. (shrink)

L’article présente le concept de déductibilité que Bolzano introduit dans sa Wissenscahftslehre, indique quelques traits caractéristiques en vertu desquels ce concept diffère de plusieurs conceptions contemporaines de la conséquence et examine l’affirmation selon laquelle il présente une forte similarité avec la conception de Tarski et la logique de la pertinence.The article presents the concept of deducibility which Bolzano introduced in his Wissenschaftslehre, points out some of the characteristic features in virtue of which it differs from many modern conceptions of consequence (...) and examines the claims that it displays a strong similarity to Tarski’s account and relevance logic. (shrink)

I begin by formulating the problem of the nature of fallacy in terms of the logic of the negative evaluation of argument, that is, in terms of a theory of logical criticism; here I discuss several features of my approach and several advantages vis-à-vis other approaches; a main feature of my approach is the concern to avoid both formalist and empiricist excesses. I then define six types of fallaciousness, labeled formal, explanatory, presuppositional, positive, semantical, and persuasive; they all involve arguments (...) whose conclusion may be said not to follow from the premises, that is, they involve the logical evaluation of relationships among propositions. I also provide a set of data consisting of four historical cases or nine specific instances of fallacious arguments; these all pertain to the Copernican controversy about the earth's motion in the seventeenth century. I end with a discussion of further problems and inquiries that deserve attention. (shrink)

Jesus has been accused of committing a fallacy (of denying the antecedent) at John 8:47. Careful analysis of this text (1) reveals a hitherto unrecognized valid form of argument which can superficially look like the predicate-logic analogue of denying the antecedent; (2) shows that determining whether a published text can be fairly charged with committing a fallacy may require (but often does not get) extensive and detailed analysis; (3) acquits Jesus of the charge; and thereby (4) conflnns a claim by (...) Michael Burke that published arguments can seldom be fairly charged with denying the antecedent, or analogous fallacies. (shrink)

We are pleased to release this edition of Ralph Johnson’s The Rise of Informal Logic as Volume 2 in the series Windsor Studies in Argumentation. This edition is a reprint of the previous Vale Press edition with some typographical errors and other minor mistakes corrected. The prime motive for gathering Ralph H. Johnson’s essays under one cover is their clear articulation of the goals, concerns and problems of the discipline of informal logic. To my knowledge all of the published articles, (...) even of the 1980s, are still in print. But some are obtainable only by special request of a journal back issue. Their availability, even their existence, is not nearly widely enough known, and this volume is dedicated to remedying that disservice to those currently working in the field of informal logic, critical thinking, argumentation, and practical reasoning. Three of these sixteen pieces appear here in print for the first time. The previously published pieces have appeared from 1980 to 1992 as chapters in collective works or as articles in journals, and these in turn published in Canada, USA, The Netherlands and Belgium. It is hoped that gathering this hitherto scattered material under one cover will contribute to a greater understanding of what informal logic is, and to an enhanced sense of the impact of Johnson’s ideas. A discipline of informal logic might exist today without the writings of Johnson and his frequent co-author, J. Anthony Blair. But it would almost certainly be quite different from what it actually is. (shrink)