Informal Fallacy

Taxonomy: Logical Fallacy > Informal Fallacy


Accident, Ambiguity, Appeal to Ignorance, Begging the Question, Black-or-White Fallacy, Composition, Division, Non Causa Pro Causa, One-Sidedness, Overgeneralization, Red Herring Fallacy, Special Pleading, Vagueness, Weak Analogy


The distinction between formal and informal fallacy is based on the distinction between form and content, specifically, between the logical form of an argument and its non-logical content. A formal fallacy is a type of argument that is fallacious solely on the basis of its logical form. In contrast, an informal fallacy is, of course, one that is not formal, that is, what makes such an argument fallacious is not purely a matter of logical form.

In addition to non-logical content, the context of an argument is also not a part of its logical form and plays a role in the fallaciousness of many of the informal fallacies. By "context", I refer to the linguistic or social setting of an argument; for instance, a particular argument may occur in the context of a debate. See the Exposure section, below, for specifics and examples.

Frequently, but not exclusively, informal fallacies occur in non-deductive reasoning, which relies on content as well as form for cogency. Also, because content is important in informal fallacies, there are cogent arguments with the form of the fallacy. For this reason, when forms are given in the entries for individual informal fallacies, this is for identification purposes only―that is, one cannot tell from the form alone that an instance is fallacious, since content is also relevant. Rather, the forms will help to differentiate between distinct types of informal fallacy.

As a logical fallacy, Informal Fallacy is the most general fallacy committed by arguments that are fallacious for informal reasons. However, a given fallacious argument would be classified as an Informal Fallacy only if it could not be given a more specific classification. For this reason, there is no Example of Informal Fallacy given; instead, see the Examples under the Subfallacies, above.


Since an informal fallacy is a type of argument whose content or context is relevant to its fallaciousness, logical fallacies can be informal for the following reasons, among others:


S. Morris Engel, With Good Reason: An Introduction to Informal Fallacies (Fifth Edition) (St. Martin's, 1994). A good textbook for beginners.