Logic of Knowledge and Utterance and the Liar

We extend the ordinary logic of knowledge based on the operator K and the system of axioms S₅ by adding a new operator U, standing for the agent utters , and certain axioms and a rule for U, forming thus a new system KU. The main advantage of KU is that we can express in it intentions of the speaker concerning the truth or falsehood of the claims he utters and analyze them logically. Specifically we can express in the new language various notions of lying, as well as of telling the truth. Consequently, as long as lying or telling the truth about a fact is an intentional mode of the speaker, we can resolve the Liar paradox, or at least some of its variants, turning it into an ordinary (false or true) sentence. Also, using Kripke structures analogous to those employed by S. Kraus and D. Lehmann in [3] for modelling the logic of knowledge and belief, we offer a sound and complete semantics for KU.     

Are there True Contradictions? A Critical Discussion of Graham Priest's, Beyond the limits of thought

The present article critically examines three aspects of Graham Priest's dialetheic analysis of very important kinds of limitations (the limit of what can be expressed, described, conceived, known, or the limit of some operation or other). First, it is shown that Priest's considerations focusing on Hegel's account of the infinite cannot be sustained, mainly because Priest seems to rely on a too restrictive notion of object. Second, we discuss Priest's treatment of the paradoxes in Cantorian set-theory. It is shown that Priest does not address the issue in full generality; rather, he relies on a reading of Cantor which implicitly attributes a very strong principle concerning quantification over arbitrary domains to Cantor. Third, the main piece of Priest's work, the so-called “inclosure schema”, is investigated. This schema is supposed to formalize the core of many well-known paradoxes. We claim, however, that formally the schema is not sound. This revised version was published online in August 2006 with corrections to the Cover Date.     

A dialogue on Zeno's paradox of Achilles and the tortoise

The five participants in this dialogue critically discuss Zeno of Elea's paradox of Achilles and the tortoise. They consider a number of solutions to and restatements of the paradox, together with their philosophical implications. Among the issues investigated include the appearance-reality distinction, Aristotle's distinction between actual and potential infinity, the concept of a continuum, Cantor's continuum hypothesis and theory of transfinite ordinals, and, as a solution to Zeno's puzzle, the distinction between infinite and indeterminate or inexhaustible divisibility.     

Framing of decisions under ambiguity

This paper reports three experiments that illustrate framing of decision problems due to Ellsberg (1961) in which probabilities are ambiguous. Although the standard Ellsberg problems often induce violations of Savage's sure-thing principle, framing of the equivalent problems in a sequential format reduces these violations. Nevertheless, this has an ironic consequence of introducing another inconsistency in the decision makers' choices: An inconsistency between the standard and sequential formulations of the Ellsberg problems.     

Phenomenological Argumentative Structure

The nontechnical ability to identify or match argumentative structure seems to be an important reasoning skill. Instruments that have questions designed to measure this skill include major standardized tests for graduate school admission, for example, the United States-Canadian Law School Admission Test (LSAT), the Graduate Record Examinations (GRE), and the Graduate Management Admission Test (GMAT). Writers and reviewers of such tests need an appropriate foundation for developing such questions – they need a proper representation of phenomenological argumentative structure – for legitimacy, and because these tests affect people's lives. This paper attempts to construct an adequate and appropriate representation of such structure, that is, the logical structure that an argument is perceived to have by mature reasoners, albeit ones who are untrained in logic.     

Argument Structure and Disciplinary Perspective

Many in the informal logic tradition distinguish convergent from linked argument structure. The pragma-dialectical tradition distinguishes multiple from co-ordinatively compound argumentation. Although these two distinctions may appear to coincide, constituting only a terminological difference, we argue that they are distinct, indeed expressing different disciplinary perspectives on argumentation. From a logical point of view, where the primary evaluative issue concerns sufficient strength of support, the unit of analysis is the individual argument, the particular premises put forward to support a given conclusion. Structure is internal to this unit. From a dialectical point of view, where the focus concerns how well a critical discussion comes to a reasoned conclusion of some disputed question, the argumentation need not constitute a single unit of argument. The unit of dialectical analysis will be the entire argumentation made up of these several arguments. The multiple/co-ordinatively compound distinction is dialectical, while the linked/convergent distinction is logical. Keeping these two pairs of distinctions separate allows us to see certain attempts to characterize convergent versus linked arguments as rather characterizing multiple versus co-ordinatively compound arguments, in particular attempts of Thomas, Nolt, and Yanal, and to resolve straightforwardly conflicts, tensions, or anomalies in their accounts. Walton's preferred Suspension/Insufficient Proof test to identify linked argument structure correctly identifies co-ordinatively compound structure. His objection to using the concept of relevance to explicate the distinction between linked and convergent structure within co-ordinatively compound argumentation can be met through explicating relevance in terms of inference licenses. His counterexample to the Suspension/No Support test for identifying linked structure which this approach supports can itself be straightforwardly dealt with when the test is explicated through inference licenses.     

Distinguishing indeterminate belief from “risk-averse” preferences

I focus my discussion on the well-known Ellsberg paradox. I find good normative reasons for incorporating non-precise belief, as represented by sets of probabilities, in an Ellsberg decision model. This amounts to forgoing the completeness axiom of expected utility theory. Provided that probability sets are interpreted as genuinely indeterminate belief (as opposed to “imprecise” belief), such a model can moreover make the “Ellsberg choices” rationally permissible. Without some further element to the story, however, the model does not explain how an agent may come to have unique preferences for each of the Ellsberg options. Levi (1986, Hard choices: Decision making under unresolved conflict. Cambridge, New York: Cambridge University Press) holds that the extra element amounts to innocuous secondary “risk” or security considerations that are used to break ties when more than one option is rationally permissible. While I think a lexical choice rule of this kind is very plausible, I argue that it involves a greater break with xpected utility theory than mere violation of the ordering axiom.     

Deductivism and the Informal Fallacies

This essay proposes and defends a general thesis concerning the nature of fallacies of reasoning. These in distinctive ways are all said to be deductively invalid. More importantly, the most accurate, complete and charitable reconstructions of these species and specimens of the informal fallacies are instructive with respect to the individual character of each distinct informal fallacy. Reconstructions of the fallacies as deductive invalidities are possible in every case, if deductivism is true, which means that in every case they should be formalizable in an expressively comprehensive formal symbolic deductive logic. The general thesis is illustrated by a detailed examination of Walter Burleigh's paradox in his c. 1323 work, De Puritate Artis Logicae Tractatus Longior (Longer Treatise on the Purity of Logic), as a challenge to the deductive validity of hypothetical syllogism. The paradox has the form, ‹If I call you a swine, then I call you an animal; if I call you an animal, then I speak truly; therefore, if I call you a swine, then I speak truly'. Several solutions to the problem are considered, and the inference is exposed as an instance of the common deductive fallacy of equivocation.     

Arguments,Meta-arguments,and Metadialogues: A Reconstruction of Krabbe,Govier, and Woods

Krabbe (2003, in F.H. van Eemeren, J.A. Blair, C.A. Willard and A.F. Snoeck Henkemans (eds.), Proceedings of the Fifth Conference of the International Society for the Study of Argumentation, Sic Sat, Amsterdam, pp. 641–644) defined a metadialogue as a dialogue about one or more dialogues, and a ground-level dialogue as a dialogue that is not a metadialogue. Similarly, I define a meta-argument as an argument about one or more arguments, and a ground-level argument as one which is not a meta-argument. Krabbe (1995, in F.H van Eemeren, R. Grootendorst, J.A. Blair, C.A. Willard and A.F. Snoeck Henkemans (eds.), Proceedings of the Third ISSA Conference on Argumentation, Sic Sat, Amsterdam, pp. 333–344) showed that formal-fallacy criticism (and more generally, fallacy criticism) consists of metadialogues, and that such metadialogues can be profiled in ways that lead to their proper termination or resolution. I reconstruct Krabbe’s metadialogical account into monolectical, meta-argumentative terminology by describing three-types of meta-arguments corresponding to the three ways of proving formal invalidity he studied: the trivial logic-indifferent method; the method of counterexample situation; and the method of formal paraphrase. A fourth type of meta-argument corresponds to what Oliver (1967, Mind 76, 463–478), Govier (1985, Informal Logic 7, 27–33), and Copi (1986) call refutation by logical analogy. A fifth type of meta-argument represents my reconstruction of arguments by parity of reasoning studied by Woods and Hudak (1989, Informal Logic 11, 125–139). Other particular meta-arguments deserving future study are Hume’s critique of the argument from design in the Dialogues Concerning Natural Religion, and Mill’s initial argument in The Subjection of Women about the importance of established custom and general feeling vis-à-vis argumentation.