Online research in philosophy

An abstract framework for structured arguments is presented, which instantiates Dung's ('On the Acceptability of Arguments and its Fundamental Role in Nonmonotonic Reasoning, Logic Programming, and n- Person Games', Artificial Intelligence , 77, 321-357) abstract argumentation frameworks. Arguments are defined as inference trees formed by applying two kinds of inference rules: strict and defeasible rules. This naturally leads to three ways of attacking an argument: attacking a premise, attacking a conclusion and attacking an inference. To resolve such attacks, preferences may be used, which leads to three corresponding kinds of defeat: undermining, rebutting and undercutting defeats. The nature of the inference rules, the structure of the logical language on which they operate and the origin of the preferences are, apart from some basic assumptions, left unspecified. The resulting framework integrates work of Pollock, Vreeswijk and others on the structure of arguments and the nature of defeat and extends it in several respects. Various rationality postulates are proved to be satisfied by the framework, and several existing approaches are proved to be a special case of the framework, including assumption-based argumentation and DefLog.

An introduction to the motivations and mechanics of John Pollock's theory of defeasible reasoning, from a lecture at the Northern Institute of Philosophy in 2010.

‘Performative’ transcendental arguments exploit the status of a subcategory of self-falsifying propositions in showing that some form of skepticism is unsustainable. The aim of this paper is to examine the relationship between performatively inconsistent propositions and transcendental arguments, and then to compare performative transcendental arguments to modest transcendental arguments that seek only to establish the indispensability of some belief or conceptual framework. Reconceptualizing transcendental arguments as performative helps focus the intended dilemma for the skeptic: performative transcendental arguments directly confront the skeptic with the choice of abandoning either skepticism or some other deep theoretical commitment. Many philosophers, from Aristotle and St. Thomas Aquinas to Jaakko Hintikka, C.I. Lewis, and Bernard Lonergan, have claimed that some skeptical propositions regarding knowledge, reason, and/or morality can be shown to be self-defeating; that is to say, they have claimed that the very upholding of some skeptical position is in some way incompatible with the position being upheld, or with the implied, broader dialectical position of the skeptic in question. Statements or propositions alleged to have this characteristic also sometimes are called ‘self-falsifying,’ ‘self-refuting,’ ‘self-stultifying,’ ‘self-destructive,’ or ‘pointless.’ However, proponents of the strategy of showing skepticism to be self-defeating have not in general adequately distinguished between two types of self-defeating proposition: self-falsifying and self-stultifying. In the first part of this paper I distinguish between self-falsifying and self-stultifying propositions, and introduce the notion of performative self-falsification. In the second part I discuss classical transcendental arguments, ‘modest’ transcendental arguments, and objections to each. In the third part I introduce two types of transcendental argument—each labeled “performative”—corresponding to two types of performatively self-falsifying proposition, and I compare them to modest transcendental arguments.

Michael Huemer has argued for the justification principle known as phenomenal conservativism by employing a transcendental argument that claims all attempts to reject phenomenal conservativism ultimately are doomed to self-defeat. My contribution presents two independent arguments against the self-defeat argument for phenomenal conservativism after briefly presenting Huemer’s account of phenomenal conservativism and the justification for the self-defeat argument. My first argument suggests some ways that philosophers may reject Huemer’s premise that all justified beliefs are formed on the basis of seemings. In the second argument I contend that phenomenal conservativism is not a well-motivated account of internal justification, which is a further reason to reject the self-defeat argument. Consequently, the self-defeat argument fails to show that rejecting phenomenal conservativism inevitably leads one to a self-defeating position.

This paper points out some problems with two recent logical systems – one due to Prakken and Sartor, the other due to Kowalski and Toni – designedfor the representation of defeasible arguments in general, but with a specialemphasis on legal reasoning.

This article begins with an introduction to defeasible (nonmonotonic) reasoning and a brief description of a computer program, EVID, which can perform such reasoning. I then explain, and illustrate with examples, how this program can be applied in computational representations of ordinary dialogic argumentation. The program represents the beliefs and doubts of the dialoguers, and uses these propositional attitudes, which can include commonsense defeasible inference rules, to infer various changing conclusions as a dialogue progresses. It is proposed that computational representations of this kind are a useful tool in the analysis of dialogic argumentation, and, in particular, demonstrate the important role of defeasible reasoning in everyday arguments using commonsense reasoning.

Plato seems to have claimed that epistemological relativism is self-defeating in two ways. As reformulated by Siegel: arguments for relativism must be advanced as either relativistically or non-relativistically sound. In either case they are dialectically ineffective for the relativist. Second, relativism is either relativistically or non-relativistically true. Either choice commits the relativist to major concessions to her opponent, or so the story goes. But the relativist can advance her arguments as non-relativistically sound, for the consumption of the non-relativist. Moreover, relativists can claim that relativism is true not only for the relativist, but for her non-relativist opponent as well. Relativism is not self-defeating in either of these ways, for much the same reasons that skepticism is not self-defeating. But we cannot live as relativists, because relativism leads to epistemic paralysis, as the example of prediction shows.

This paper argues that some traditional fallacies should be considered as reasonable arguments when used as part of a properly conducted dialog. It is shown that argumentation schemes, formal dialog models, and profiles of dialog are useful tools for studying properties of defeasible reasoning and fallacies. It is explained how defeasible reasoning of the most common sort can deteriorate into fallacious argumentation in some instances. Conditions are formulated that can be used as normative tools to judge whether a given defeasible argument is fallacious or not. It is shown that three leading violations of proper dialog standards for defeasible reasoning necessary to see how fallacies work are: (a) improper failure to retract a commitment, (b) failure of openness to defeat, and (c) illicit reversal of burden of proof.

The question addressed in this paper is how the degree of justification of a belief is determined. A conclusion may be supported by several different arguments, the arguments typically being defeasible, and there may also be arguments of varying strengths for defeaters for some of the supporting arguments. What is sought is a way of computing the “on sum” degree of justification of a conclusion in terms of the degrees of justification of all relevant premises and the strengths of all relevant reasons.

One of the most striking characteristics of human beings is their ability to function successfully in complex environments about which they know very little. In light of our pervasive ignorance, we cannot get around in the world just reasoning deductively from our prior beliefs together with new perceptual input. As our conclusions are not guaranteed to be true, we must countenance the possibility that new information will lead us to change our minds, withdrawing previously adopted beliefs. In this sense, our reasoning is “defeasible”. The question arises how defeasible reasoning works, or ought to work. In particular we need rules governing what a cognizer ought to believe given a set of interacting arguments some of which defeat others. That is what is called a “semantics” for defeasible reasoning, and this chapter will propose a new semantics that avoids certain clear counter-examples to all existing semantics.