Logical Fallacy

Exposition:

"Fallacy" is a vague and ambiguous word. First, "fallacy" is frequently used to mean a common factual error, and a number of books with it in the title—such as Tad Tuleja's Fabulous Fallacies—are collections of common factual mistakes, with corrections. This is not the type of fallacy catalogued in the Fallacy Files; rather, it is a collection of logical fallacies.

"Logical fallacy" shares with "factual fallacy" the genus "common error", that is, both are types of error commonly committed by people. Factual fallacies, of course, are mistakes about factual matters, whereas logical fallacies are not errors of fact, but errors of reasoning.

A further ambiguity in the term "logical fallacy" is that between type and instance:

1. Type: In this sense, a logical fallacy is a type of error, that is, a class of many similar instances of bad reasoning.
2. Instance: In this sense, a logical fallacy is an instance of bad reasoning, that is, a specific argument rather than a class of them.

Throughout the Fallacy Files I restrict the term "logical fallacy"—or just "fallacy", for short, since I'm not concerned here with factual mistakes—to sense 1, and not sense 2. For sense 2, I say that a particular argument "commits" a fallacy, or that it is "fallacious", which means that the argument is an instance of a fallacy, in sense 1.

Nonetheless, "fallacy" is still ambiguous because errors in reasoning are of many distinct types, and it is vague because some types of logical error are matters of degree. Roughly speaking, though, I will use the following definition:

Logical Fallacy = a common type of error in reasoning.

Subfallacies: The Taxonomy of Logical Fallacies

Resource:

Madsen Pirie, The Book of the Fallacy: A Training Manual for Intellectual Subversives (Routledge and Kegan Paul, 1985). This book is, unfortunately, out of print and used copies are difficult to find, but it is the only single volume that covers logical fallacies in general, that is, formal as well as informal ones.