On argument strength

Everyday life reasoning and argumentation is defeasible and uncertain. I present a probability logic framework to rationally reconstruct everyday life reasoning and argumentation. Coherence in the sense of De Finetti is used as the basic rationality norm. I discuss two basic classes of approaches to construct measures of argument strength. The first class imposes a probabilistic relation between the premises and the conclusion. The second class imposes a deductive relation. I argue for the second class, as the first class is problematic if the arguments involve conditionals. I present a measure of argument strength that allows for dealing explicitly with uncertain conditionals in the premise set. Probabilistic approaches to argumentation became popular in various fields including argumentation theory (e.g., Hahn & Oaksford, 2006), formal epistemology (e.g., Pfeifer, 2007, 2008), the psychology of reasoning (e.g., Hahn & Oaksford, 2007), and computer science (e.g., Haenni, 2009).