In the late summer of 1998, the authors, a cognitive scientist and a logician, started talking about the relevance of modern mathematical logic to the study of human reasoning, and we have been talking ever since. This book is an interim report of that conversation. It argues that results such as those on the Wason selection task, purportedly showing the irrelevance of formal logic to actual human reasoning, have been widely misinterpreted, mainly because the picture of logic current in psychology (...) and cognitive science is completely mistaken. We aim to give the reader a more accurate picture of mathematical logic and, in doing so, hope to show that logic, properly conceived, is still a very helpful tool in cognitive science. The main thrust of the book is therefore constructive. We give a number of examples in which logical theorizing helps in understanding and modeling observed behavior in reasoning tasks, deviations of that behavior in a psychiatric disorder (autism), and even the roots of that behavior in the evolution of the brain. (shrink)

Develops a logical analysis of dialogue in which two or more parties attempt to advance their own interests. It includes a classification of the major types of dialogues and a discussion of several important informal fallacies.

This paper offers a solution to the problem of understanding how a fallacious argument can be deceptive by “seeming to be valid”, or (better) appearing to be a better argument of its kind than it really is. The explanation of how fallacies are deceptive is based on heuristics and paraschemes. Heuristics are fast and frugal shortcuts to a solution to a problem that sometimes jump to a conclusion that is not justified. In fallacious instances, according to the theory proposed, this (...) jump overlooks prerequisites of the defeasible argumentation scheme for the type of argument in question. Three informal fallacies, argumentum ad verecundiam , argumentum ad ignorantiam and fear appeal argument, are used to illustrate and explain the theory. (shrink)

Bayesian reasoning has been applied formally to statistical inference, machine learning and analysing scientific method. Here I apply it informally to more common forms of inference, namely natural language arguments. I analyse a variety of traditional fallacies, deductive, inductive and causal, and find more merit in them than is generally acknowledged. Bayesian principles provide a framework for understanding ordinary arguments which is well worth developing.

In this article, we argue for the general importance of normative theories of argument strength. We also provide some evidence based on our recent work on the fallacies as to why Bayesian probability might, in fact, be able to supply such an account. In the remainder of the article we discuss the general characteristics that make a specifically Bayesian approach desirable, and critically evaluate putative flaws of Bayesian probability that have been raised in the argumentation literature.

Behavioral scientists routinely publish broad claims about human psychology and behavior in the world's top journals based on samples drawn entirely from Western, Educated, Industrialized, Rich, and Democratic (WEIRD) societies. Researchers – often implicitly – assume that either there is little variation across human populations, or that these “standard subjects” are as representative of the species as any other population. Are these assumptions justified? Here, our review of the comparative database from across the behavioral sciences suggests both that there is (...) substantial variability in experimental results across populations and that WEIRD subjects are particularly unusual compared with the rest of the species – frequent outliers. The domains reviewed include visual perception, fairness, cooperation, spatial reasoning, categorization and inferential induction, moral reasoning, reasoning styles, self-concepts and related motivations, and the heritability of IQ. The findings suggest that members of WEIRD societies, including young children, are among the least representative populations one could find for generalizing about humans. Many of these findings involve domains that are associated with fundamental aspects of psychology, motivation, and behavior – hence, there are no obviousa priorigrounds for claiming that a particular behavioral phenomenon is universal based on sampling from a single subpopulation. Overall, these empirical patterns suggests that we need to be less cavalier in addressing questions ofhumannature on the basis of data drawn from this particularly thin, and rather unusual, slice of humanity. We close by proposing ways to structurally re-organize the behavioral sciences to best tackle these challenges. (shrink)

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)

Short abstract (98 words). Reasoning is generally seen as a means to improve knowledge and make better decisions. However, much evidence shows that reasoning often leads to epistemic distortions and poor decisions. This suggests that the function of reasoning should be rethought. Our hypothesis is that the function of reasoning is argumentative. It is to devise and evaluate arguments intended to persuade. Reasoning so conceived is adaptive given humans’ exceptional dependence on communication and vulnerability to misinformation. A wide range of (...) evidence in the psychology of reasoning and decision making can be reinterpreted and better explained in the light of this hypothesis. (shrink)

The paper argues that the two best known formal logical fallacies, namely denying the antecedent (DA) and affirming the consequent (AC) are not just basic and simple errors, which prove human irrationality, but rather informational shortcuts, which may provide a quick and dirty way of extracting useful information from the environment. DA and AC are shown to be degraded versions of Bayes’ theorem, once this is stripped of some of its probabilities. The less the probabilities count, the closer these fallacies (...) become to a reasoning that is not only informationally useful but also logically valid. (shrink)

The term "non-monotonic logic" covers a family of formal frameworks devised to capture and represent defeasible inference , i.e., that kind of inference of everyday life in which reasoners draw conclusions tentatively, reserving the right to retract them in the light of further information. Such inferences are called "non-monotonic" because the set of conclusions warranted on the basis of a given knowledge base does not increase (in fact, it can shrink) with the size of the knowledge base itself. This is (...) in contrast to classical (first-order) logic, whose inferences, being deductively valid, can never be "undone" by new information. (shrink)

A revision of a sermon on the evils of calling model theory “semantics”, preached at Notre Dame on Saint Patrick’s Day, 2005. Provisional version: references remain to be added. To appear in Mathematics, Modality, and Models: Selected Philosophical Papers, coming from Cambridge University Press.

There was a long tradition in philosophy according to which good reasoning had to be deductively valid. However, that tradition began to be questioned in the 1960’s, and is now thoroughly discredited. What caused its downfall was the recognition that many familiar kinds of reasoning are not deductively valid, but clearly confer justification on their conclusions. Here are some simple examples.

The object of this paper is to show why recent research in the psychology of deductive and probabilistic reasoning does not have.

In the international bestseller, Thinking, Fast and Slow, Daniel Kahneman, the renowned psychologist and winner of the Nobel Prize in Economics, takes us on a groundbreaking tour of the mind and explains the two systems that drive the way we think. System 1 is fast, intuitive, and emotional; System 2 is slower, more deliberative, and more logical. The impact of overconfidence on corporate strategies, the difficulties of predicting what will make us happy in the future, the profound effect of cognitive (...) biases on everything from playing the stock market to planning our next vacation—each of these can be understood only by knowing how the two systems shape our judgments and decisions. -/- Engaging the reader in a lively conversation about how we think, Kahneman reveals where we can and cannot trust our intuitions and how we can tap into the benefits of slow thinking. He offers practical and enlightening insights into how choices are made in both our business and our personal lives—and how we can use different techniques to guard against the mental glitches that often get us into trouble. Winner of the National Academy of Sciences Best Book Award and the Los Angeles Times Book Prize and selected by The New York Times Book Review as one of the ten best books of 2011, Thinking, Fast and Slow is destined to be a classic. (shrink)

The New Rhetoric is founded on the idea that since “argumentation aims at securing the adherence of those to whom it is addressed, it is, in its entirety, relative to the audience to be influenced,” says Chaïm Perelman and L. Olbrechts-Tyteca, and they rely, in particular, for their theory of argumentation on the twin concepts of universal and particular audiences: while every argument is directed to a specific individual or group, the orator decides what information and what approaches will achieve (...) the greatest adherence according to an ideal audience. This ideal, Perelman explains, can be embodied, for example, "in God, in all reasonable and competent men, in the man deliberating or in an elite.” Like particular audiences, then, the universal audience is never fixed or absolute but depends on the orator, the content and goals of the argument, and the particular audience to whom the argument is addressed. These considerations determine what information constitutes "facts" and "reasonableness" and thus help to determine the universal audience that, in turn, shapes the orator's approach. /// The adherence of an audience is also determined by the orator's use of values, a further key concept of the New Rhetoric. Perelman's treatment of value and his view of epideictic rhetoric sets his approach apart from that of the ancients and of Aristotle in particular. Aristotle's division of rhetoric into three genres–forensic, deliberative, and epideictic–is largely motivated by the judgments required for each: forensic or legal arguments require verdicts on past action, deliberative or political rhetoric seeks judgment on future action, and epideictic or ceremonial rhetoric concerns values associated with praise or blame and seeks no specific decisions. For Aristotle, the epideictic genre was of limited importance in the civic realm since it did not concern facts or policies. Perelman, in contrast, believes not only that epideictic rhetoric warrants more attention, but that the values normally limited to that genre are in fact central to all argumentation. "Epideictic oratory," Perelman argues, "has significant and important argumentation for strengthening the disposition toward action by increasing adherence to the values it lauds.” These values are central to the persuasiveness of arguments in all rhetorical genres since the orator always attempts to "establish a sense of communion centered around particular values recognized by the audience.”. (shrink)

In Between Facts and Norms, Jürgen Habermas works out the legal and political implications of his Theory of Communicative Action (1981), bringing to fruition the project announced with his publication of The Structural Transformation of the Public Sphere in 1962. This new work is a major contribution to recent debates on the rule of law and the possibilities of democracy in postindustrial societies, but it is much more. The introduction by William Rehg succinctly captures the special nature of the work, (...) noting that it offers a sweeping, sociologically informed conceptualization of law and basic rights, a normative account of the rule of law and the constitutional state, an attempt to bridge normative and empirical approaches to democracy, and an account of the social context required for democracy. Finally, the work frames and caps these arguments with a bold proposal for a new paradigm of law that goes beyond the dichotomies that have afflicted modern political theory from its inception and that still underlie current controversies between so-called liberals and civic republicans. The book includes a postscript written in 1994, which restates the argument in light of its initial reception, and two appendixes, which cover key developments that preceded the book. Habermas himself was actively involved in the translation, adapting the text as necessary to make it more accessible to English-speaking readers. (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)

Hamblin held that the conception of 'fallacy' as an argument that seems valid but is not really so was the dominant conception of fallacy in the history of fallacy studies. The present paper explores the extent of support that there is for this view. After presenting a brief analysis of 'the standard definition of fallacy,' a number of the definitions of 'fallacy' in texts from the middle of this century – from the standard treatment – are considered. This is followed (...) by a review of the definitions of 'fallacy' in the earlier history of logic books, including those of Aristotle, Whately, Mill and De Morgan. The essay concludes that there is scarcely any support for Hamblin's view that this particular definition of 'fallacy' was widely held. (shrink)

The paper shows why and how an empirical study of fast-and-frugal heuristics can provide norms of good reasoning, and thus how (and how far) rationality can be naturalized. We explain the heuristics that humans often rely on in solving problems, for example, choosing investment strategies or apartments, placing bets in sports, or making library searches. We then show that heuristics can lead to judgments that are as accurate as or even more accurate than strategies that use more information and computation, (...) including optimization methods. A standard way to defend the use of heuristics is by reference to accuracy-effort trade-offs. We take a different route, emphasizing ecological rationality (the relationship between cognitive heuristics and environment), and argue that in uncertain environments, more information and computation are not always better (the “less-can-be-more” doctrine). The resulting naturalism about rationality is thus normative because it not only describes what heuristics people use, but also in which specific environments one should rely on a heuristic in order to make better inferences. While we desist from claiming that the scope of ecological rationality is unlimited, we think it is of wide practical use. (shrink)

The introduction of the concept of strategic maneuvering into the pragma-dialectical theory makes it possible to formulate testable hypotheses regarding the persuasiveness of argumentative moves that are made in argumentative discourse. After summarizing the standard pragma-dialectical approach to argumentation, van Eemeren, Garssen, and Meuffels explain what the extension of the pragma-dialectical approach with strategic maneuvering involves and discuss the fallacies in terms of the extended pragma-dialectical approach as derailments of strategic maneuvering. Then they give an empirical interpretation of the extended (...) pragma-dialectical model in which they report the testing of three hypotheses which formulate preliminary conditions for effectiveness research within the framework of the extended pragma-dialectical theory and the results of the tests they consecutively carried out. (shrink)

Saul Kripke has made fundamental contributions to a variety of areas of logic, and his name is attached to a corresponding variety of objects and results. 1 For philosophers, by far the most important examples are ‘Kripke models’, which have been adopted as the standard type of models for modal and related non-classical logics. What follows is an elementary introduction to Kripke’s contributions in this area, intended to prepare the reader to tackle more formal treatments elsewhere.2 2. WHAT IS A (...) MODEL THEORY? Traditionally, a statement is regarded as logically valid if it is an instance of a logically valid form, where a form is regarded as logically valid if every instance is true. In modern logic, forms are represented by formulas involving letters and special symbols, and logicians seek therefore to define a notion of model and a notion of a formula’s truth in a model in such a way that every instance of a form will be true if and only if a formula representing that form is true in every model. Thus the unsurveyably vast range of instances can be replaced for purposes of logical evaluation by the range of models, which may be more tractable theoretically and perhaps practically. Consideration of the familiar case of classical sentential logic should make these ideas clear. Here a formula, say (p & q) ∨ ¬p ∨ ¬q, will be valid if for all statements P.. (shrink)

In this paper two theories of defeasible reasoning, Pollock's account and my theory of ranking functions, are compared, on a strategic level, since a strictly formal comparison would have been unfeasible. A brief summary of the accounts shows their basic difference: Pollock's is a strictly computational one, whereas ranking functions provide a regulative theory. Consequently, I argue that Pollock's theory is normatively defective, unable to provide a theoretical justification for its basic inference rules and thus an independent notion of admissible (...) rules. Conversely, I explain how quite a number of achievements of Pollock's account can be adequately duplicated within ranking theory. The main purpose of the paper, though, is not to settle a dispute with formal epistemology, but rather to emphasize the importance of formal methods to the whole of epistemology. (shrink)

We examine in detail three classic reasoning fallacies, that is, supposedly ``incorrect'' forms of argument. These are the so-called argumentam ad ignorantiam, the circular argument or petitio principii, and the slippery slope argument. In each case, the argument type is shown to match structurally arguments which are widely accepted. This suggests that it is not the form of the arguments as such that is problematic but rather something about the content of those examples with which they are typically justified. This (...) leads to a Bayesian reanalysis of these classic argument forms and a reformulation of the conditions under which they do or do not constitute legitimate forms of argumentation. (shrink)

Toulmin’s formulation of “analytic arguments” in his 1958 book, The Uses of Argument, is opaque. Commentators have not adequately explicated this formulation, though Toulmin called it a “key” and “crucial” concept for his model of argument macrostructure. Toulmin’s principle “tests” for determining analytic arguments are problematic. Neither the “tautology test” nor the “verification test” straightforwardly indicates whether an argument is analytic or not. As such, Toulmin’s notion of analytic arguments might not represent such a key feature of his model. Absent (...) a clearer formulation of analytic arguments, readers of Toulmin should be hesitant to adopt this terminology. (shrink)

The study of deductive reasoning has been a major paradigm in psychology for approximately the past 40 years. Research has shown that people make many logical errors on such tasks and are strongly influenced by problem content and context. It is argued that this paradigm was developed in a context of logicist thinking that is now outmoded. Few reasoning researchers still believe that logic is an appropriate normative system for most human reasoning, let alone a model for describing the process (...) of human reasoning, and many use the paradigm principally to study pragmatic and probabilistic processes. It is suggested that the methods used for studying reasoning be reviewed, especially the instructional context, which necessarily defines pragmatic influences as biases. (shrink)

The appeal to expert opinion is an argument form that uses the verdict of an expert to support a position or hypothesis. A previous scheme-based treatment of the argument form is formalized within a Bayesian network that is able to capture the critical aspects of the argument form, including the central considerations of the expert's expertise and trustworthiness. We propose this as an appropriate normative framework for the argument form, enabling the development and testing of quantitative predictions as to how (...) people evaluate this argument, suggesting that such an approach might be beneficial to argumentation research generally. We subsequently present two experiments as an example of the potential for future research in this vein, demonstrating that participants' quantitative ratings of the convincingness of a proposition that has been supported with an appeal to expert opinion were broadly consistent with the predictions of the Bayesian model. (shrink)

This paper is an exercise in intellectual history, an attempt to understand how a specific term—”informal logic”— came to be interpreted in so many different ways. I trace the emergence and development of “informal logic” to help explain the many different meanings, how they emerged and how they are related. This paper is also, to some degree, an account of a movement that developed outside the mainstream of philosophy, whose origins lie in a desire to make logic useful (echoing Dewey).

Chaïm Perelman and Lucie Olbrechts-Tyteca founded the Brussels school of argumentation in 1958, when they published their famous Traité de l'argumentation. Even if, in Brussels, Eugène Dupréel had already set out to rehabilitate the Sophists, the intellectual atmosphere in the French-speaking world was not very propitious for rhetoric. Most French intellectuals were plunged into ideological debates linked to the intellectual monopoly of the French communist party on societal issues. Free discussion was certainly not very topical. It was only after the (...) fall of the Berlin wall in 1989, five years after Perelman's death, that rhetoric began to draw increasing attention. His ideas then gained momentum in France, as .. (shrink)

This article reacts against the undesirable ideological separation between dialectical and rhetorical approaches to argumentative discourse. It argues that a sound evaluation of argumentation requires an analysis that reveals all aspects of the discourse pertinent to critical testing. To explain the rationale of the various moves made in the discourse and the strategic patterns behind them, not only the interlocutors' dialectical goals must be taken into account, but also their rhetorical goals. After explaining how rhetorical insight can be instrumental in (...) deepening and justifying a dialectical analysis, an integrated analysis is made of the rhetorical strategies that are brought to bear in an advertorial published by the oil company Shell. (shrink)

In this paper, it is argued that the most fruitful approach to developing normative models of argument quality is one that combines the argumentation scheme approach with Bayesian argumentation. Three sample argumentation schemes from the literature are discussed: the argument from sign, the argument from expert opinion, and the appeal to popular opinion. Limitations of the scheme-based treatment of these argument forms are identified and it is shown how a Bayesian perspective may help to overcome these. At the same time, (...) the contributions of the standard scheme-based approach are highlighted, and it is argued that only a combination of the insights of different traditions will yield a complete normative theory of argument quality. (shrink)

The Handbook of the Logic of Argument and Inference is an authoritative reference work in a single volume, designed for the attention of senior undergraduates, graduate students and researchers in all the leading research areas concerned with the logic of practical argument and inference. After an introductory chapter, the role of standard logics is surveyed in two chapters. These chapters can serve as a mini-course for interested readers, in deductive and inductive logic, or as a refresher. Then follow two chapters (...) of criticism; one the internal critique and the other the empirical critique. The first deals with objections to standard logics (as theories of argument and inference) arising from the research programme in philosophical logic. The second canvasses criticisms arising from work in cognitive and experimental psychology. The next five chapters deal with developments in dialogue logic, interrogative logic, informal logic, probability logic and artificial intelligence. The last chapter surveys formal approaches to practical reasoning and anticipates possible future developments. Taken as a whole the Handbook is a single-volume indication of the present state of the logic of argument and inference at its conceptual and theoretical best. Future editions will periodically incorporate significant new developments. (shrink)

Rhetorical analyses typically characterize structural, topical, and stylistic features of written or spoken argumentative text, and may also consider the context of interaction as well as the epistemic and social standing of participants as these relate to the goals of gaining, sustaining, and strengthening an audience’s adherence to a thesis or a course of action. Such considerations, broadly conceived, are taken to constitute rhetorical insights, insofar as they bear on effecting audience persuasion or, for that matter, fail to do so. (...) In the following, I am concerned with the question what a normative approach to argumentation may stand to gain from rhetorical insights. First, I follow Thomas Conley .. (shrink)

A warrant may be grounded in personal testimony, technical method, or public consensus. The justified choice of a field, in authorizing the warrant and providing further extension of support constitutes a legitimation inference. Complex cases evolve when there are a surplus of good reasons as potential support for a claim, and a choice must be made either to select a single ground for the claim or to advance independently valid reasons, differentially grounded, as support. Complex cases enter the realm of (...) controversy when not all relevant grounds offer the same degree of support or point in the same direction, and a choice to select some grounds and discard others must be justified. The justification of the selection of grounds constitutes a legitimation warrant—a missing element of the Toulmin model. (shrink)

Bayesian reasoning has been applied formally to statistical inference, machine learning and analysing scientific method. Here I apply it informally to more common forms of inference, namely natural language arguments. I analyse a variety of traditional fallacies, deductive, inductive and causal, and find more merit in them than is generally acknowledged. Bayesian principles provide a framework for understanding ordinary arguments which is well worth developing.