Informal Logic and Fallacies

Informal logic evaluates the reasoning of everyday and persuasive arguments, including the analysis of fallacies—patterns of argument that seem cogent but are not.

Definition

Informal logic is the study of the norms and analysis of arguments expressed in ordinary language, including the identification and assessment of fallacies, the recurring ways arguments go wrong.

Scope

This topic covers the informal logic movement and the theory of fallacies. It treats the standards of relevance, sufficiency, and acceptability for evaluating natural-language arguments; the traditional and modern catalogs of fallacies; Hamblin's critique of the standard treatment; and pragmatic and dialectical reconceptions of fallacy as failures within argumentative exchange.

Core questions

• By what criteria should everyday arguments be judged good or bad?
• What makes a fallacy fallacious, and are fallacies always errors?
• Can fallacies be reliably catalogued and identified?
• How does informal logic relate to critical thinking pedagogy?

Key concepts

• relevance, sufficiency, acceptability
• ad hominem
• begging the question
• straw man
• argumentation scheme misuse

Key theories

Critique of the standard treatment

Hamblin argues that the traditional list-based account of fallacies is theoretically impoverished, defining fallacies merely as arguments that seem valid but are not, and calls for a more rigorous basis.

Pragmatic theory of fallacy

Walton reconceives fallacies as misuses of legitimate argumentation schemes within a dialogue, so that whether a move is fallacious depends on its context and conversational goals.

History

The modern study of fallacies was reinvigorated by Hamblin's 1970 book, which exposed the incoherence of the inherited textbook treatment. The informal logic movement, centered in Canada around Johnson and Blair, developed criteria for argument evaluation and a critical-thinking pedagogy from the 1970s. Walton's pragmatic and dialectical work reframed fallacies as context-dependent failures rather than fixed forms.

Debates

Are fallacies real errors or context-dependent?

A central dispute is whether named fallacies pick out genuinely defective forms or whether the same move can be reasonable or fallacious depending on dialogue context, as pragmatic theories hold.

Key figures

• C. L. Hamblin
• Douglas Walton
• Ralph Johnson
• J. Anthony Blair

Seminal works

• hamblin1970
• walton1995

Frequently asked questions

Is every fallacy always a bad argument?

Not necessarily. Many theorists now hold that a move such as an appeal to authority or to emotion can be legitimate in some contexts and fallacious in others, so identifying a pattern is only the start of evaluation.