Overdefinition

Overdefinition refers to a definition that attaches the name of a term to a broader set of things than intended. In semantics and philosophy, a term is overdefined when the definiens includes members outside the term’s intended extension, or when nonessential properties are treated as essential. The effect is a definition that is too inclusive, leading to misclassification and ambiguity.

A classic example appears in geometry: defining a square as a quadrilateral with four equal sides is technically overbroad because it would also include rhombuses that are not squares unless the definition also requires right angles. The standard geometric definition is a quadrilateral with four equal sides and four right angles.

Overdefinition can arise from using vague or overlapping properties, conflating necessary with sufficient conditions, or attempting to cover obvious cases at once. It can hinder communication, impede formal reasoning, and complicate dictionaries or taxonomies by widening the category beyond its conventional scope.

Overdefinition is related to, but distinct from, underdefinition (defining a term too narrowly) and from overgeneralization in linguistics, where a form is extended beyond its customary usage. In logic and formal analysis, overdefinition often signals that the chosen criteria for a term’s application are too broad or insufficiently constrained.

To prevent overdefinition, definitions should state precise necessary and sufficient conditions and, where appropriate, clarify scope with careful notes and examples. Distinguishing essential properties from incidental features helps maintain clarity and consistency in reasoning and communication.