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叛教。
天主教背教者（或叛教者），[1]也称冷淡教友，是指那些早年领洗加入天主教，但已经离开教会，甚至已改宗其他宗教之人士。[2]根据天主教教义和法律，他们仍然被视为天主教徒。[3][4][5]
冷淡教友是指那些“丧失信仰或不守教规”之教友，[1]他们在婴儿或学校领洗后不知所终，或成人领洗后离开了教会。[6]
从教义与教会法角度看，背教者仍然是天主教教徒。按照《天主教教理》，圣洗圣事在基督徒身上留下了不可磨灭的精神印记，表示他属于基督。任何罪恶也消除不了这个印记。[4]因此一位离开天主教或很少继续去参与天主教活动的受洗者会被称为冷淡天主教徒而非前天主教徒。如果一个天主教教徒背教后重新恢复信仰，他们不需要再改宗，仅需参加成年人入门礼仪来更新信仰。[5]
天主教保禄修会出版社《天主教法典新注释》指出：
一旦领洗、加入天主教，他就永远是天主教教友（
semel catholicus semper catholicus）。当中改信其他宗教的，即使成为
无神论者或
不可知论者，甚至被
逐出教会，仍被视为天主教徒。
[5]
美国天主教神父兼资深传媒人里斯承认当地教友出走问题严重，他更引民调数据指出，背教者数目已占全国天主教人口三分之一。离开天主教人士当中，接近一半没再参加任何宗教组织，另接近一半则改信基督新教。[7]
Kinkel, R.J. (2008), Cinderella Church: the Story of Early Christianity, introduction: "In the old days (1950s) these people would be called backsliders, apostates, lapsed Christians, and now this label has emerged: FARC, ie fallen away Roman Catholic."
Barbernitz, P. (1993), Parish Ministry for Returning Catholics, p3, "'I'm Catholic' is also the statement frequently used by some other people — those whom others might have named 'inactive' Catholics, 'fallen-away' or 'lapsed' Catholics. For many of them, the statement remains, 'I'm Catholic.'"
《天主教教理》第1272条：“受过洗的人，因圣洗而与基督结成一体，肖似基督。圣洗为基督徒盖上不可磨灭的灵性印记(神印)，表示他隶属于基督。虽然罪恶能阻碍圣洗结出救恩的果实，但任何罪恶都不能拭去这印记。”
Beal, J.P., New Commentary on the Code of Canon Law, "Once a Catholic by baptism or reception, one always remains a Catholic (semel catholicus semper catholicus). Even those who have joined another religion, have become atheists or agnostics, or have been excommunicated remain Catholics. Excommunicates lose rights, such as the right to the sacraments, but they are still bound to the obligations of the law; their rights are restored when they are reconciled through the remission of the penalty."
Reese, Thomas (2011), The hidden exodus: Catholics becoming Protestants （页面存档备份，存于互联网档案馆）, National Catholic Reporter, "The number of people who have left the Catholic church is huge...One of three people who were raised Catholic no longer identifies as Catholic...Almost half of those leaving the church become unaffiliated and almost half become Protestant."
