Circular Definition

(Latin, circulus in definiendo), a logical fallacy, in which a certain concept (or term) A is defined by means of another concept (term) B, although B, in turn, cannot be defined without using A. Such a “circular chain of terms” may consist of more than two links—and the more terms it contains, the more hidden the circularity may be. Like circular argument, circular definition is a variant of the general concept of vicious circle (Latin, circulus vitiosus). Circular “definitions,” since they do not reduce the definiendum to the definiens, are not, strictly speaking, definitions. It should be kept in mind, however, that the mere mention of the definiendum in the definiens does not necessarily produce circularity; examples of this are definitions by induction.