Informal logic

Lore & Background

Informal logic as a named enterprise emerged roughly in the mid-20th century as a sub-field of philosophy. Blair and Johnson's keynote address included an appendix listing 13 problems and issues that defined the scope of the field, including the theory of logical criticism, the theory of argument, the theory of fallacy, and the relationship of informal logic to other inquiries. Proposed definitions vary. Johnson and Blair define informal logic as 'a branch of logic whose task is to develop non-formal standards, criteria, procedures for the analysis, interpretation, evaluation, criticism and construction of argumentation.' Frans H. van Eemeren writes that the label covers 'a collection of normative approaches to the study of reasoning in ordinary language that remain closer to the practice of argumentation than formal logic.' The precise definition remains a matter of dispute.

Reader's Guide

Informal logic matters because it addresses the practical need for reasoning skills in everyday life, media analysis, and political discourse. It arose from a pedagogical shift in the mid-20th century, when philosophers like Howard Kahane sought to enable students to cope with misleading rhetoric and dissect arguments in ordinary language. Informal logic is associated with informal fallacies, critical thinking, the thinking skills movement, and argumentation theory. It abandons the notion of logical form as key to understanding argument structure and retires validity as the central normative standard, instead considering arguments where the conclusion is supported beyond reasonable doubt—such as conductive arguments used in law.

Did You Know?

• The precise definition of 'informal logic' is a matter of some dispute.