The “Logic” of Informal Logic

Abstract

The purpose of the chapter is to explore some historically-offered possible answers to the question of what alternatives there might be to deduction and induction. I briefly describe and characterize six accounts that seem on the face of it to portray some third type of assessment of an illative move, independent of deductive validity and of inductive strength: those of Wisdom, Toulmin, Wellman, Rescher, defeasible reasoning theorists such as Pollock, and Walton. I then compare these accounts under eight headings. I conclude that the parallel and largely independent development of theories of defeasible reasoning and informal approaches to argument interpretation and appraisal seem to put beyond doubt the empirical fact of such reasoning and argument and to argue for its bona fides. The proposition that such reasoning and arguments are legitimate, one of the founding hypotheses of the informal logic movement, seems to have found fairly widespread confirmation.