Someone told me that if an infant is baptized Catholic, but is raised Protestant, and then converts back to Catholicism as an adult, he can’t become a priest. Is this true?
It probably comes from this canon law, however a heresy must be imputable to be a delict. This requires an act of will. The person may not have learned the Catholic faith, although baptized so this is significant. In any case, there would be an investigation upon application for seminary.
CIC
Can. 1041 The following are irregular for receiving orders:
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2/ a person who has committed the delict of apostasy, heresy, or schism;
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IRREGULARITIES AND SIMPLE IM PEDIMENTS IN THE NEW CODE OF CANON LAW BY THE JEV. JOHN J. RICKEY, S.T.B., J.C.L. (MARCH 18, 1920.)
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“Heresy is a species of infidelity in men who, having professed the faith of Christ, corrupt its dogmas.” 7 “The heretical tenets may be adhered to from involuntary causes: inculpable ignorance of the true creed, erroneous judgment, imperfect apprehension and comprehension of dogmas. In none of these does the will play an appreciable part, wherefore one of the necessary conditions of sinfulness free choice is wanting and such heresy is merely objective, or material. On the other hand, the will may freely incline the intellect to adhere to tenets declared false by the divine teaching authority of the Church. The impelling motives are many: intellectual pride or exaggerated reliance on ones own in sight, the illusions of religious zeal, the allurements of political or ecclesiastical power, the ties of material interests and personal status ; and perhaps others more dishonorable. Heresy thus willed is imputable to the subject and carries with it various degrees of guilt; it is called formal because to the material error it adds the informative element of freely willed. Pertinacity, that is, obstinate adhesion to a particular tenet, is required to make heresy formal.” 8 The Code does not specify any particular species, hence one who is heretical in any sense, must contract this irregularity.
7 St. Thomas, II-II, Q. xi, a. i.
8 Catholic Encyclopedia, art. Heresy.