differentiam

Differentiam is a term used in classical logic and philosophy to denote the distinguishing characteristic that sets a species apart from other species within the same genus. In the Aristotelian and scholastic tradition, a proper definition of a species is formed by giving its genus and its differentia; the genus provides the general category, while the differentia specifies what makes this species unique within that category. The differentia should express an essential attribute rather than an accidental one.

The word derives from Latin differentia, meaning "difference." Differentiam is the accusative form used in Latin phrasing, such as "the differentiam of homo" or "the differentiam of the species." In English scholarship, the term is often Anglicized as "the differentia" when describing the defining feature.

Examples commonly cited include: for humans, genus "animal" and differentia "rational" (man is a rational animal); for a triangle, genus "polygon" and differentia "three-sided." These examples illustrate how the differentia functions to carve out a precise extension from among related forms.

In modern philosophy and logic, the genus–differentia framework has influenced definitional theory and taxonomy, though contemporary practice often emphasizes necessary and sufficient conditions, set-theoretic definitions, or property lists rather than a fixed Aristotelian schema.

See also: genus, species, Porphyrian tree, definition.