The contribution critically discusses Walton's argumentation scheme approach. On the one hand, its enormous richness and closeness to the empirical argumentation material is appreciated, but, on the other, fundamental conceptual weaknesses are revealed. Although the approach more recently has been declared to strive for “true beliefs and correct choices” it has not systematically developed the proposed schemes in a way that these goals are reached. Accordingly, many proposed schemes are fallacious from an epistemological standpoint.

My thesis situates itself within the field of the Philosophy of Worldviews. Specifically, it aims to address the normative question of what the task should be of such a philosophy when faced with the problem of conflicting beliefs between religious worldviews. To answer this question, I turn to the procedure of aporetical analysis, in short, aporetics. Firstly, aporetics offers a distinct method of consistency restoration within inconsistent sets on the basis of thesis rejection and thesis modification. Secondly, aporetics leads to (...) an understanding of the availability of aporetic exits on the basis of epistemic criteria. On the one hand, this leads us to opt for an orientational monism/pluralism, which steers the middle course between the epistemic stances of exclusivism and pluralism. On the other hand, it allows us to identify epistemic criteria for worldview acquisition on the basis of three distinct superclasses. These superclasses can be derived from Jürgen Habermas' validity claims, and applied to the self-understanding of contemporary theories of religion. (shrink)

In this overview article, we first explain what we take informal logic to be, discussing misconceptions and distinguishing our conception of it from competing ones; second, we briefly catalogue recent informal logic research, under 14 headings; third, we suggest four broad areas of problems and questions for future research; fourth, we describe current scholarly resources for informal logic; fifth, we discuss three implications of informal logic for philosophy in particular, and take note ofpractical consequences of a more general sort.

In all three of its manifestations, —abusive, circumstantial and tu quoque—the role of the ad hominem is to raise a doubt about the opposite party’s casemaking bona-fides.Provided that it is both presumptive and provisional, drawing such a conclusion is not a logical mistake, hence not a fallacy on the traditional conception of it. More remarkable is the role of the ad hominem retort in seeking the reassurance of one’s opponent when, on the face of it, reassurance is precisely what he (...) would seem to be ill-placed to give. Brief concluding remarks are given over to an examination of rival approaches to the ad hominem, especially those in which it is conceived of as a dialectical error. (shrink)

This paper develops a logical theory that unifies all three standard types of argumentative attack in AI, namely rebutting, undercutting and undermining attacks. We build on default justification logic that already represents undercutting and rebutting attacks, and we add undermining attacks. Intuitively, undermining does not target default inference, as undercutting, or default conclusion, as rebutting, but rather attacks an argument’s premise as a starting point for default reasoning. In default justification logic, reasoning starts from a set of premises, which is (...) then extended by conclusions that hold by default. We argue that modeling undermining defeaters in the view of default theories requires changing the set of premises upon receiving new information. To model changes to premises, we give a dynamic aspect to default justification logic by using the techniques from the logic of belief revision. More specifically, undermining is modeled with belief revision operations that include contracting a set of premises, that is, removing some information from it. The novel combination of default reasoning and belief revision in justification logic enriches both approaches to reasoning under uncertainty. By the end of the paper, we show some important aspects of defeasible argumentation in which our logic compares favorably to structured argumentation frameworks. (shrink)

Douglas Walton has done extensive and valuable work on the concepts of presumption and practical reasoning. However, Walton’s attempt to model practical reasoning as presumptive is misguided. The notions of “inference” and of the burden of proof shifting back and forth between proponent and respondent are misleading and lead to counterintuitive consequences. Because the issue in practical reasoning is a proposal, not a proposition, there are, in the standard case, several perfectly good reasons on both sides simultaneously, which implies that (...) argument appraisal necessarily contains a subjective element—a fact argumentation theory needs to conceptualize. (shrink)

One takes one’s word that p when a source vouches for p and one accepts the word of that source. If the source is reliable in this case, p is acceptable. The reliability of the source is a measure of its plausibility. If a source has the relevant competence, credibility, authority, that word is acceptable. Likewise, the word may be acceptable if accompanied by a cogent argument, but presumption may be misplaced. One may recognize a presumption for a statement when (...) such recognition is not justified, the positive version of the fallacy. One may refuse to recognize a presumption for a statement when there really is a presumption for the statement, the negative version of the fallacy. The essay proceeds to explore various dimensions of when it is justified to take a source’s word for a claim, and when it is justified to reject a claim from a source. The discussion ranges over considerations of sexism and race, cultural differences, and the relationship of presumptions to fallacies. Also considered is the role of trust in taking someone’s word and the factors involved in trusting someone. (shrink)