APOSTASY (άπόστασις), denoting in classic Greek (Herodotus, Thucydides) a defection or revolt from a military commander, is generally employed to describe a complete renunciation of the Christian faith. In the first centuries of the Christian era, apostasy was most commonly induced by persecution, and was indicated by some outward act, such as offering incense to a heathen deity or blaspheming the name of Christ. The Emperor Julian, who is known in history as The Apostate, abandoned Christianity for paganism soon after assuming the purple, though it is questionable whether he had ever really embraced the Christian faith. In the Roman Catholic Church the word apostasy is also applied to the renunciation of monastic vows (apostasis a monachatu), and to the abandonment of the clerical profession for the life of the world (apostasis a clericatu). Of the latter class a celebrated instance was Talleyrand.

a deserting or abandoning of the true religion. The word is borrowed from the Latin _apostatare_, or _apostare_, _to despise_ or _violate_ any thing. Hence _apostatare leges_ anciently signified _to transgress the laws_. The Latin _apostatare_, again, comes from ἀπὸ, _from_, and ἳϛημι, _I stand_. Among the Romanists, apostasy also signifies the forsaking of a religious order, whereof a man had made profession, without a lawful dispensation. The ancients distinguished three kinds of apostasy: the first, _a supererogatione_, is committed by a priest, or religious, who abandons his profession, and returns to his lay state; the second, _a mandatis Dei_, by a person of any condition, who abandons the commands of God, though he retains his faith; the third, _a fide_, by him who not only abandons his works, but also the faith. There is this difference between an apostate and a heretic; that the latter only abandons a part of the faith, whereas the former renounces the whole. The primitive Christian church distinguished several kinds of apostasy. The first was that of those who relapsed from Christianity into Judaism; the second, that of those who blended Judaism and Christianity together; and the third was that of those who, after having been Christians, voluntarily relapsed into Paganism.