Heresy (Gr. hairesis) primitively means a choice or election, and in its application to religious belief is used to designate as well the act of choosing for one's self, and maintaining opinions contrary to the authorised teaching of the religious community to which one's obedience is due, as also the heterodox opinions thus adopted and the party which may have adopted them. In the Acts of the Apostles (see v. 17, xv. 5, xxiv. 5, xxviii. 22) the word seems to be used of a sect or party, apart from the consideration of its character, whether good or bad; but in the Epistles and in the early Christian writers it is almost invariably used in a bad sense, which is the sense uniformly accepted in all subsequent theological literature. Roman Catholic writers, regarding the authority of their own church as supreme and final, apply the name of heresy to any formal denial of a doctrine proposed by the Roman Catholic Church as necessary to be believed. Protestant writers seldom use the word, except in relation to what each sect regards as the essentials of Christian faith.
Even in the apostolic times heresies had arisen in the church, and before the Council of Nice the catalogue of sects had already swelled to considerable dimensions. The chief early heresies are reducible to two classes: (1) those which attempted to associate the Christian doctrines with Judaism; (2) those which ingrafted Christianity upon the Gentile religions or the Gentile philosophies.
From the very date of the establishment of Christianity in the Roman empire heresy appears to have been regarded as a crime cognisable by the civil law; and Constantine enacted several severe laws for its repression, which were continued and extended by his successors, and were collected into a single title, De Hæreticis, in the Justinian code. The penalties of heresy ordained by these enactments are very severe, extending to corporal punishment, and even to death; and they all proceed on the distinct assumption that a crime against religion is a crime against the state. These enactments of the Roman law were embodied in the various codes of the European kingdoms; in English law heresy consisted in holding opinions contrary to Catholic faith and the determination of Holy Church. By common law the offender was to be tried in the provincial synod by the archbishop and his council, and, after conviction, was to be given up to the king to be dealt with at his pleasure. But the statute 2 Hen. IV. chap. 15 (De hæretico comburendo) empowered the diocesan to take cognisance of heresy, and, on conviction, to hand over the criminal directly, and without waiting for the king's writ, to the sheriff or other competent officer. This statute continued practically in force, with certain modifications, till the 29 Charles II. chap. 9, since which time heresy is left entirely to the cognisance of the ecclesiastical courts. The article BLASPHEMY deals with an important cognate subject.
In the case of clergy of the Church of England, under a statute of 1571 (now confined to its narrowest effect by a series of judgments) any distinct contradiction of the Articles, or obvious evasion of them, subjects the offender to deprivation of his benefit. The supreme authority is the Judicial Committee of the Privy-council, which construes the articles and formularies according to the legal rules for the interpretation of statutes (see ECCLESIASTICAL COURTS; and ENGLAND, CHURCH OF). In the Presbyterian churches a heretical minister is usually tried by his presbytery, and may be deposed from the ministry by the General Assembly.
For the history and literature of heretical sects, consult the very numerous articles in this work on the various bodies of heretics, as ALBIGENSES, ARIUS, EBIONITES, ESSENES, GNOTICS, MANICHEANS, MONTANUS, MYSTICS, PELAGIUS, &c. See also the articles BAUR, CHURCH HISTORY, DOMINICANS, EXCOMMUNICATION, INQUISITION, PERSECUTION; the standard ecclesiastical historians; Arnold's Ketzehistorie (1699); Hahn's Ketzer im Mittelalter (1850); and Hilgenfeld's Ketzergeschichte des Urchristentums (1883).