Informal logic is an attempt to develop a logic that can assess and analyze the arguments that occur in natural language discourse. Discussions in the field may address instances of scientific, legal, and other technical forms of reasoning, but the overriding aim has been a comprehensive account of argument that can explain and evaluate the arguments found in discussion, debate and disagreement as they manifest themselves in daily life — in social and political commentary; in news reports and editorials in (...) the mass media ; in advertising and corporate and governmental communications; and in personal exchange. (shrink)

In the first part of this paper I make some general remarks about the relevance of semantics and pragmatics to argumentation theory, insisting on the importance of the reconstruction of speaker meaning for argument analysis, especially in the case of implicatures. In the second part of the paper I look more closely at the relation between argument and implicature. In the last part I discuss the concept of argumentative implicature, that is, implicatures that are generated by speech acts of arguing. (...) I maintain, against Jackson (1987), that there are no specifically argumentative implicatures. (shrink)

Recent work on conditional reasoning argues that denying the antecedent [DA] and affirming the consequent [AC] are defeasible but cogent patterns of argument, either because they are effective, rational, albeit heuristic applications of Bayesian probability, or because they are licensed by the principle of total evidence. Against this, we show that on any prevailing interpretation of indicative conditionals the premises of DA and AC arguments do not license their conclusions without additional assumptions. The cogency of DA and AC inferences rather (...) depends on contingent factors extrinsic to, and independent of, what is asserted by DA and AC arguments. arguments do not license their conclusions without additional assumptions. The cogency of DA and AC inferences rather depends on contingent factors extrinsic to, and independent of, what is asserted by DA and AC arguments. (shrink)

The standard account of denying the antecedent (DA) is that it is a deductively invalid form of argument, and that, in a conditional argument, to argue from the falsity of the antecedent to the falsity of the consequent is always fallacious. In this paper, we argue that DA is not always a fallacious argumentative strategy. Instead, there is a legitimate usage of DA according to which it is a defeasible argument against the acceptability of a claim. The dialectical effect of (...) denying the antecedent is to shift the burden of proof back to the original proponent of a claim. We provide a model of this non-fallacious usage which is built upon pragmatic models of argumentation. (shrink)

The precedent studies on the validity of Modus ponens and Modus tollens have been carried out with most regard to a major type of conditionals in which the conditional clause is a sufficient condition for the main clause. But we sometimes, in natural language arguments, find other types of conditionals in which the conditional clause is a necessary or necessary and sufficient condition for the main clause. In this paper I reappraise, on the basis of new definitions of Modus ponens (...) and Modus tollens, their validity/invalidity in natural language arguments in consideration of all types of conditionals. (shrink)

: In this paper we examine two challenges to the orthodox understanding of the fallacy of denying the antecedent. One challenge is to say that passages thought to express the fallacy can usually be given an interpretation on which they express valid arguments, entitling us to query whether the fallacy is commonly, if ever, committed at all. We discuss this claim in Section 1. The second challenge comes from those who think that there are legitimate uses of denying the antecedent (...) that have traditionally been overlooked. In Section 2 we propose a general test for claims of this sort, and assess three versions of this view. (shrink)

In this paper I am concerned with the analysis of fragments of a discourse or text that express arguments suspected of being denials of the antecedent. I first argue that one needs to distinguish between two senses of ‘the argument expressed’. Second, I show that, with respect to one of these senses, given a Gricean account of the pragmatics of conditionals, some such fragments systematically express arguments that are valid.

This paper suggests that the flaw in the enthymeme approach to argument analysis is in the requirement, as I come to formulate it, that an argument be restated as a premises-and-conclusion sequence. The paper begins by investigating how logicians show that there are problems with the enthymeme approach. That investigation reveals a failure on the part of logicians to appreciate the importance of the rhetorical context of an argument. This failure, it is argued, is a consequence of what I refer (...) to as the Premise-Conclusion Requirement. (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)

It has been argued that a fragment of discourse that constitutes a fallacy of denying the antecedent at the level of what is literally said may not be a fallacy at the level of speaker meaning. The pragmatic phenomenon involved here is known as conditional perfection. I argue that the account of conditional perfection in van der Auwera and Horn has several problems, and I discuss several possible alternatives.