Haeresis

Haeresis (Greek: αἵρεσις, haíresis) is a term with roots in ancient Greek meaning "a choosing," "a pick," or "a faction." It originally referred to a choice or selection, sometimes used to describe a school of opinion within a group. In Hellenistic and early Christian usage, haeresis took on a technical sense as a "sect" or "party" with distinctive beliefs.

In Christian theology, haeresis became the technical designation for beliefs considered divergent from the accepted faith. The practice of identifying, debating, and combating such beliefs is known as haeresiology. Throughout late antiquity and the medieval period, various movements—such as Arianism, Gnosticism, Marcionism, Nestorianism, and Monophysitism—were described as haereses by opponents; ecumenical councils established orthodox doctrine in opposition to them.

The modern English term "heresy" stems from Latin haeresis, via Old French. The term is now often used in a historical or polemical sense to denote doctrinal deviation rather than moral fault; many scholars emphasize its social and ecclesial context rather than endorsing any pejorative value.

In contemporary scholarship, haeresis is discussed as a phenomenon within religious and philosophical communities, distinguishing orthodoxy from heterodoxy and examining how groups define, defend, and police boundaries of belief. See also: heresy, orthodoxy, heterodoxy, haeresiology.