Natural language argument, the fallacies, and p-logic

Frank Zenker

Department of Philosophy, Lund University, Sweden


This tutorial reviews the main contemporary approaches to natural language argument, explains the role these approaches assign to the fallacies, and contrasts this with applications of probability theory (aka "p-logic") to select fallacies.

As John Woods (2000: 15) put it: "Formal logic is a theory of logical forms; and informal logic is all the rest." Informal logicians (e.g., Johnson, 2000; Blair, 2012) as well as proponents of the Pragma-dialectical school of argumentation (van Eemeren & Grootendorst, 2014; van Eemeren, 2010) tend to view "all the rest" as shouldering the real work in the analysis and evaluation of natural language argumentation.
Indeed, many reject formal methods. In place of the proof techniques of the truth-functional calculus, for instance, typical resources rather include argument diagrams, schemes, and the fallacies. Similarly, rather than endorsing soundness (premise truth and deductive inferential validity) as a standard of good argument, informal logicians speak of cogency (premise acceptability, relevance, and inferential sufficiency).
In the 1960s, this anti-formalist stance arose in reaction to the only widely available formal apparatus being first-order deductive logic. The breath of formal resources available today, however, makes a continued disenchantment with them at least questionable. In fact, their neglect deprives of useful resources in appraising defeasible reasoning and argument in ways that let formal and informal realign resources.


The tutorial starts by reviewing the informal resources. We particularly study the role of the fallacies (Hamblin, 1970) in Walton’s (1995; 2010) dialogical approach, and reconstruct the rules for critical discussion in the Pragma-dialectical model, whose consensualism particularly epistemologists have criticized (Biro & Siegel, 1997; Lumer, 2010). This critique demarcates an import difference, and entails a distinct view on what the fallacies are (not) (Woods, 2013a,b).
Against this background, we offer a brief technical introduction to probability theory (p-logic), then apply it to give an analysis of argument cogency. This not only clarifies a core concept of informal logic. P-logic also provides an important corrective to its usual applications. In application to select (alleged) fallacies, indeed, formal and informal normative approaches to natural language argumentation can align.
Building on groundwork by Oaksford and Hahn (2004) and Korb (2004), among others, this contributes to a burgeoning area of research that successfully applies probabilistic reasoning to natural language argumentation. It also supplements recent work by Hahn and Hornikx (2016), for instance, who use p-logic to formalize argument schemes such as those proposed by Walton, Reed, and Macagno (2008).

Please note: The three tutorial sessions build on each other. Rather than pick one or two sessions, participants would do well to attend all three. We provide learning materials in class as online resources; there is no prior reading assignment. A background in formal logic or probability theory is neither required nor harmful to profit from the tutorial. The main learning outcome is the improved ability to orient oneself within the field of argumentation studies, and correctly apply p-logic to such crucial notions as argument cogency, fallacy, or argument strength, among others.
 

References
  • Blair, J.A. (2012). Relevance, acceptability and sufficiency today. In Groundwork in the theory of argumentation (pp. 87-100). Dordrecht: Springer.
  • Corner, A., & Hahn, U. (2013). Normative theories of argumentation: Are some norms better than others? Synthese, 190, 3579-3610.
  • Eemeren, F. H. van, and Grootendorst, R. (2004). A systematic theory of argumentation: the pragma-dialectical approach. Cambridge, UK: Cambridge University Press.
  • Eemeren, F. H. van (2010). Strategic Maneuvering in Argumentative Discourse. Extending the pragma-dialectical theory of argumentation. Amsterdam: John Benjamins.
  • Godden, D., and Zenker F. (2015). Denying antecedents and affirming consequents: The state of the art. Informal Logic, 35, 88-134.
  • Godden, D.M., and Zenker, F. (2016). A probabilistic analysis of argument cogency. Synthese (online first).
  • Hahn, U., & Hornikx, J. (2016). A normative framework for argument quality: Argumentation schemes with a Bayesian foundation. Synthese, 193, 1833-1873.
  • Hahn, U., & Oaksford, M. (2006a). A Bayesian approach to informal argument fallacies. Synthese, 152, 207-236.
  • Hahn, U., & Oaksford, M. (2006b). A normative theory of argument strength. Informal Logic, 26, 1-24.
  • Hamblin, C. (1970). Fallacies. London: Methuen.
  • Johnson, R. (2000). Manifest rationality: A pragmatic theory of argument. Mahwah, NJ: Lawrence Earbaum.
  • Korb, K. (2004). Bayesian informal logic and fallacy. Informal Logic, 24, 41-70.
  • Lumer, C. (2010). Pragma-Dialectics and the Function of Argumentation. Argumentation 24: 41-69.
  • Siegel, H. and Biro, J (1997). Epistemic Normativity, Argumentation, and Fallacies. Argumentation 11:277-292.
  • Walton, D. N. (1995). A Pragmatic Theory of Fallacy. Tuscaloosa: University of Alabama Press.
  • Walton, D. N. (2010). Why Fallacies Appear to be Better Arguments Than They Are. Informal Logic, 30 (2): 159–184.
  • Walton, D.N., Reed, C., and Macagno, F. (2008). Argumentation Schemes. New York: Cambridge University Press.
  • Woods, J. (2000). How philosophical is informal logic? Informal Logic, 20, 139-167.
  • Woods, J. (2013a). Errors of Reasoning: Naturalizing the Logic of Inference. London: College Publications.
  • Woods, J. (2013b). Epistemology Mathematicized. Informal Logic, 33 (2), 292-331.
  • Zenker, F. (2007). Changes in Conduct-rules and Ten Commandments: Pragma-dialectics 1984 vs. 2004. F. H. van Eemeren (ed.), Proceedings of the International Society for the Study of Argumentation (ISSA) Amsterdam 2006 (pp. 1581-1589). Amsterdam: SicSat.
  • Zenker, F. (2016b). The polysemy of ‘fallacy’—or ‘bias’, for that matter. In Bondy, P., and Benaquista, L. (eds). Argumentation, Objectivity and Bias (Proceedings of the 11th Conference of the Ontario Society for the Study of Argumentation, 18-21 May, 2016) (pp. 1–14). Windsor, ON: OSSA.

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