Informal fallacy
An error in reasoning whose flaw depends on content, context, or language rather than the argument’s formal logical structure.
Argument: A set of statements in which some claims are offered as reasons for another claim. Informal fallacies are defects in arguments, not merely false statements.
Ad hominem: A fallacy that attacks a person instead of addressing that person’s argument. It substitutes criticism of a speaker for evidence against the claim.
Formal fallacy: An error in deductive reasoning that follows from an invalid logical form. Unlike an informal fallacy, its defect can be identified from structure alone.
Critical thinking: The disciplined evaluation of claims, evidence, assumptions, and reasoning. Recognizing informal fallacies is one tool for evaluating arguments carefully.
Aristotle: An ancient Greek philosopher whose works shaped logic, ethics, metaphysics, and natural philosophy. His Sophistical Refutations is an early systematic study of deceptive arguments.
Premise: A statement offered as support for a conclusion in an argument. Many informal fallacies hide a weakness in the argument’s supporting claims.
Straw man: A fallacy that misrepresents an opponent’s position to make it easier to attack. The argument appears to refute a position that was never actually defended.
Cognitive bias: A systematic tendency in judgment that can produce departures from accurate reasoning. Bias is a pattern of thought; a fallacy is a defect in an argument.
Argumentation theory: The study of how arguments are constructed, interpreted, and evaluated in communication. It examines fallacies in the contexts where arguments are actually made.
Sophistical Refutations: Aristotle’s treatise analyzing arguments that appear to refute an opponent but do not. It classifies deceptive reasoning patterns that later traditions called fallacies.