Abstract

This chapter focuses on one of the common fallacies in Western philosophy called four terms (FT). The fallacy of FT violates the very first rule of constructing a valid syllogism: any syllogism must contain three and only three terms. These terms have, since Aristotle, been called the major, the minor, and the middle. The major and minor are also called the “extremes” of a syllogism, since they lie on either extreme of the middle term. In a valid syllogism, the major and minor terms are related in the conclusion, and their relation is absolutely necessary and completely justified by the premises alone. When there are four terms, either the terms are unrelated and no deduction is possible, or there are multiple syllogisms. It is clear also that in every syllogism either both or one of the premises must be like the conclusion.