The main finding of a comprehensive empirical research project on the intersubjective acceptability of the pragma-dialectical discussion rules (Van Eemeren, Garssen & Meuffels, 2009) is that ordinary language users judge discussion moves that are considered fallacious from an argumentation-theoretical perspective as unreasonable. In light of this finding it is remarkable that in everyday argumentative discourse fallacies occur regularly and seem many times not to be noticed by the participants in the discourse. This also goes for the abusive argumentum ad hominem. (...) While abusive ad hominem attacks are judged to be very unreasonable discussion moves when the unreasonableness of clear cases of this fallacy is rated in experiments, in real life this fallacy remains undetected more often than not. In this paper it is argued that this paradox can be explained by analysing abusive ad hominem attacks as a mode of strategic manoeuvring which takes on a reasonable appearance in real life situations when it mimics, as it often does, legitimate critical reactions to authority argumentation. The hypothesis that abusive fallacies are seen as less unreasonable when they are presented as if they are critical questions pertaining to the argument scheme for authority argumentation than when they are clear cases was tested systematically in two experiments. The results of these experiments confirmed the hypothesis. (shrink)

In this classic work, Leo Strauss examines the problem of natural right and argues that there is a firm foundation in reality for the distinction between right and wrong in ethics and politics. On the centenary of Strauss's birth, and the fiftieth anniversary of the Walgreen Lectures which spawned the work, _Natural Right and History_ remains as controversial and essential as ever. "Strauss... makes a significant contribution towards an understanding of the intellectual crisis in which we find ourselves... [and] brings (...) to his task an admirable scholarship and a brilliant, incisive mind."—John H. Hallowell, _American Political Science Review_ Leo Strauss was the Robert Maynard Hutchins Distinguished Service Professor Emeritus in Political Science at the University of Chicago. (shrink)

In ‘A Non-Pragmatic Vindication of Probabilism’, Jim Joyce attempts to ‘depragmatize’ de Finetti’s prevision argument for the claim that our partial beliefs ought to satisfy the axioms of probability calculus. In this paper, I adapt Joyce’s argument to give a non-pragmatic vindication of various versions of David Lewis’ Principal Principle, such as the version based on Isaac Levi's account of admissibility, Michael Thau and Ned Hall's New Principle, and Jenann Ismael's Generalized Principal Principle. Joyce enumerates properties that must be had (...) by any measure of the distance from a set of partial beliefs to the set of truth values; he shows that, on any such measure, and for any set of partial beliefs that violates the probability axioms, there is a set that satisfies those axioms that is closer to every possible set of truth values. I replace truth values by objective chances in his argument; I show that for any set of partial beliefs that violates the probability axioms or a version of the Principal Principle, there is a set that satisfies them that is closer to every possible set of objective chances. (shrink)

One of the fundamental problems of epistemology is to say when the evidence in an agent’s possession justifies the beliefs she holds. In this paper and its prequel, we defend the Bayesian solution to this problem by appealing to the following fundamental norm: Accuracy An epistemic agent ought to minimize the inaccuracy of her partial beliefs. In the prequel, we made this norm mathematically precise; in this paper, we derive its consequences. We show that the two core tenets of Bayesianism (...) follow from the norm, while the characteristic claim of the Objectivist Bayesian follows from the norm along with an extra assumption. Finally, we consider Richard Jeffrey’s proposed generalization of conditionalization. We show not only that his rule cannot be derived from the norm, unless the requirement of Rigidity is imposed from the start, but further that the norm reveals it to be illegitimate. We end by deriving an alternative updating rule for those cases in which Jeffrey’s is usually supposed to apply. (shrink)

One of the fundamental problems of epistemology is to say when the evidence in an agent’s possession justifies the beliefs she holds. In this paper and its sequel, we defend the Bayesian solution to this problem by appealing to the following fundamental norm: Accuracy An epistemic agent ought to minimize the inaccuracy of her partial beliefs. In this paper, we make this norm mathematically precise in various ways. We describe three epistemic dilemmas that an agent might face if she attempts (...) to follow Accuracy, and we show that the only inaccuracy measures that do not give rise to such dilemmas are the quadratic inaccuracy measures. In the sequel, we derive the main tenets of Bayesianism from the relevant mathematical versions of Accuracy to which this characterization of the legitimate inaccuracy measures gives rise, but we also show that Jeffrey conditionalization has to be replaced by a different method of update in order for Accuracy to be satisfied. (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.

Argument quality has consistently been shown to have strong and lasting persuasive effects. The question is what criteria people use to distinguish strong from weak arguments and how these criteria relate to the ones proposed in normative argumentation theory. In an experiment 235 participants without training in argumentation theory rated the acceptance of 30 claims about the desirability of a consequence that were supported by either an argument from analogy, from authority, or from consequences. The supporting arguments were systematically manipulated (...) to violate argument type specific criteria. Participants proved sensitive to the violation of most, but not all, argument type specific criteria. From a normative perspective these findings suggest that people act in a fairly adequate way. These findings also enable a more precise description of what people may do when critically appraising arguments, which has important implications for the use of argument quality as a methodological tool in persuasion research. (shrink)

The notion of “the burden of proof” plays an important role in real-world argumentation contexts, in particular in law. It has also been given a central role in normative accounts of argumentation, and has been used to explain a range of classic argumentation fallacies. We argue that in law the goal is to make practical decisions whereas in critical discussion the goal is frequently simply to increase or decrease degree of belief in a proposition. In the latter case, it is (...) not necessarily important whether that degree of belief exceeds a particular threshold (e.g., ‘reasonable doubt’). We explore the consequences of this distinction for the role that the “burden of proof” has played in argumentation and in theories of fallacy. (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)

Argumentation is pervasive in everyday life. Understanding what makes a strong argument is therefore of both theoretical and practical interest. One factor that seems intuitively important to the strength of an argument is the reliability of the source providing it. Whilst traditional approaches to argument evaluation are silent on this issue, the Bayesian approach to argumentation (Hahn & Oaksford, 2007) is able to capture important aspects of source reliability. In particular, the Bayesian approach predicts that argument content and source reliability (...) should interact to determine argument strength. In this paper, we outline the approach and then demonstrate the importance of source reliability in two empirical studies. These experiments show the multiplicative relationship between the content and the source of the argument predicted by the Bayesian framework. (shrink)

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.

Book Review of Luc Bovens and Stephan Hartmann *Bayesian Epistemology* by Erik J. Olsson.