Apostasy (/əˈpɒstəsi/; Greek: ἀποστασία apostasía, 'a defection or revolt') is the formal disaffiliation from, abandonment of, or renunciation of a religion by a person. It can also be defined within the broader context of embracing an opinion that is contrary to one's previous religious beliefs. One who undertakes apostasy is known as an apostate. Undertaking apostasy is called apostatizing (or apostasizing – also spelled apostacizing). The term apostasy is used by sociologists to mean the renunciation and criticism of, or opposition to, a person's former religion, in a technical sense, with no pejorative connotation. ~ Wikipedia


Heresy is any belief or theory that is strongly at variance with established beliefs or customs, in particular the accepted beliefs of a church or religious organization. The term is usually used in reference to violations of important religious teachings, but is also used of views strongly opposed to any generally accepted ideas. A heretic is a proponent of heresy. ~Wikipedia

Is it possible to be a heretic and not an apostate and vice versa? What about in other religions like Islam?

  • this might go better on philosophy SE
    – depperm
    Dec 16, 2022 at 17:35
  • Why do you say that? "Philosophy is the handmaid of religion" ~ Saint Thomas Aquinas. Dec 16, 2022 at 17:43
  • Heresy - a holding to certain views contrary to authoritative works or people in a religion, while still claiming the religion Apostasy - outright rejection of the religion
    – Luke Hill
    Dec 16, 2022 at 18:01
  • So a Christian heretic is still a Christian while a Christian apostate isn't a Christian. Gracias. Dec 16, 2022 at 18:06
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    @depperm I disagree. Having studied both, theology defines apostasy and heresy. Philosophy does not.
    – eques
    Dec 16, 2022 at 19:01

1 Answer 1


Apostasy and Heresy are always defined relative to the perspective of a religion or a religion's sect/denomination. Since we are dealing with many denominations and many religions, this answer is about the common meaning of those 2 terminologies that most denominations / religions use.

The Wikipedia articles you cited are quite clear in the definitions:

  • Heresy: belief that is strongly at variance with established beliefs
  • Apostasy: renunciation or abandonment of a religion

Can one be a heretic but not an apostate, or vice versa?

Of course one can. Let's say I am a Unitarian who has never been a Catholic. From the Catholic Church point of view, I am NOT an apostate since I have never been a Catholic, but I AM a heretic since by being a Unitarian I'm rejecting the belief in one of the most central dogmas of Catholicism: the Trinity.

If later I take a further step in denying Christianity altogether then the Catholic Church will call me an apostate because I used to be a Christian, albeit a "heretical" one. Similarly, if I am a Presbyterian and I decide to become a Buddhist, I would be an apostate from the Presbyterian Church's point of view because I abandon Christianity. Since I am no longer a Christian, I can no longer be called a heretic from any Christian denomination's point of view. Thus I can be an apostate but not a heretic.

But let's say I'm a Protestant who converts to Catholicism. I may or may not be called a heretic depending on how stringent my previous church is. This is because of ecumenism effort in the late 20th century where as long as someone belongs to a mainstream Christian group he/she can usually switch between mainstream groups without incurring the label heretic. But several non-denominational churches with a fundamentalist tendency can still call me a heretic if I become a Catholic.

Can one be an apostate while STILL professing to be a Christian?

YES, but this would be apostasy in a DIFFERENT sense: behavioral instead of intellectual. The extensive and detailed Wikipedia article Apostasy in Christianity covers the behavioral aspect in its sections on Biblical teaching, Patristic teaching, Reformers' teaching, as well as provide links to specific denomination's view. Some examples of "behavioral" apostasy:

  1. Bible's imagery of Israel's breaking covenant relationship with God through disobedience to the law (Jer 2:19-29) or worshipping other gods in addition to YHWH (Judges 2:19, Jer 2:1-3, Eze 16)
  2. Early church fathers' labelling of these behaviors as "apostasy" although the Christians were not renouncing their beliefs (see this article section for details):
    • Persistent and willful immorality, rivalry & envy that split the community, refusing to be corrected
    • Denying Christ out of fear (but not in their heart) during persecutions
    • Being extremely deceived by false teachers until the faith is no longer recognizably Christian; thus it is MORE than heresy (in Patristic understanding, heresy is "walking a different path", i.e. following non-orthodox but still recognizably Christian such as following Arian teaching)

What about in other religions like Islam?

In my limited understanding, if a Moslem converts to become a Christian, he/she would be an apostate from all Moslem groups' point of view. But if a Sunni Moslem becomes a Shia Moslem, that may or may not qualify him/her of being a heretical Moslem (see Quora answer Do Sunnis and Shiites see each other as heresy?) See also the article Heresy in Islam describing how belonging to one of the smaller Islam sects (such as the Alawis, or the Sufis) may count as heresy from the point of view of a larger group such as the Wahhabis.


  • The occasions where one is called an apostate are relative to the religion you used to belong.
  • The occasions where one is called a heretic are relative to another group within the same religion that you currently belong.
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    You may be a heretic, but at least you're not a heresiarch!
    – Peter Turner
    Dec 16, 2022 at 18:55
  • Muchas gracias. So if I leave Christianity, I'm an apostate, but if I, for instance, refuse to endorse the Holy Trinity, I'm a heretic. 🙂 Dec 16, 2022 at 18:58
  • @AgentSmith Assuming you currently belongs to one of the mainstream Christian groups, yes 🙂. But I doubt that your ex-Christian friend will call you that to your face; they would try to address your concerns and win you back. But as PeterTurner said, at least you're not the founder of a heresy :-). Dec 16, 2022 at 19:01
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    I would have to agree. According to Wikipedia, Issac Newton didn't believe in the Trinity, but he is also described as a devout Christian. Dec 17, 2022 at 4:52
  • 1
    @AgentSmith You asked "Is it true that Christians had more problems with heresy than apostasy while the converse is true for Islam?" It appears so since, according to a 2015 study, more Muslims converted to Christianity than vice versa. Also Christianity has been dealing with heresies since the very first century starting with Gnosticism and to 20th century with New Age, Oneness Pentecostal, etc. Maybe the freedom in Christian countries since 1648 contributed to new heresies being produced. Dec 17, 2022 at 5:49

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