 Being able to detect and avoid fallacies has been viewed as a supplement to criteria of good reasoning. The knowledge of fallacies is needed to arm us against the most enticing missteps we might take with arguments—so thought not only Aristotle but also the early nineteenth century logicians Richard Whately and John Stuart Mill. But as the course of logical theory from the late nineteenth-century forward turned more and more to axiomatic systems and formal languages, the study of reasoning and natural language argumentation received much less attention, and hence developments in the study of fallacies almost came to a standstill. Until well past the middle of the twentieth century, discussions of fallacies were for the most part relegated to introductory level textbooks. It was only when philosophers realized the ill fit between formal logic, on the one hand, and natural language reasoning and argumentation, on the other, that the interest in fallacies has returned. Since the 1970s the utility of knowing about fallacies has been acknowledged (Johnson and Blair 1993), and the way in which fallacies are incorporated into theories of argumentation has been taken as a sign of a theory’s level of adequacy (Biro and Siegel 2007, van Eemeren 2010).