Informal logic

Informal logic is a branch of logic concerned with the principles of logical thought as they apply outside formal settings, though its precise definition is debated. Ralph H. Johnson and J. Anthony Blair define it as a branch of logic tasked with developing non-formal standards, criteria, and procedures for analyzing, interpreting, evaluating, criticizing, and constructing argumentation. This field is closely associated with informal fallacies, critical thinking, and argumentation theory. Frans H. van Eemeren describes informal logic as a collection of normative approaches to studying reasoning in ordinary language that remain closer to the practice of argumentation than formal logic.

The field emerged as a distinct philosophical sub-field in the mid-20th century, initially motivated by pedagogical concerns. Textbooks from this era, such as Howard Kahane’s *Logic and Contemporary Rhetoric* (1971), rejected symbolic approaches to logic for general audiences, focusing instead on practical reasoning in everyday life, including analyzing media and political rhetoric. Other influential early texts included Michael Scriven’s *Reasoning* and Johnson and Blair’s *Logical Self-Defense*. Earlier precursors include Monroe Beardsley’s *Practical Logic* and Stephen Toulmin’s *The Uses of Argument*. The field became established through the First International Symposium on Informal Logic in 1978, whose keynote appendix outlined thirteen key problems, including the theory of fallacy, the ethics of argumentation, and the relationship of informal logic to other inquiries. Since 1983, the journal *Informal Logic* has been the field’s primary publication, with other journals such as *Argumentation* and *Philosophy and Rhetoric* also regularly publishing relevant articles.