ECclesiastical Habit — A plain cassock with a ferraiolo.
In any case, the priest’s habit must be a cassock when he celebrates Mass (can. 811, § 1); religious must wear the habit proper to their order, unless the superior grants permission (can. 596). It is forbidden to anyone else to wear the ecclesiastical or religious habit (can. 492, § 3 and 683); clerics reduced to the lay state may not wear it (can. 213, § 1), nor may those to whom its use has been forbidden as a penalty for some offence (can. 2300, 2304, 2305), nor, in the case of a religious habit, those who have been dismissed or secularised (can. 639–640).
Serious canonical penalties exist against clerics who, without legitimate reason, fail to wear the prescribed ecclesiastical habit (can. 136 § 3, 188 n. 7, 2379); from this it is rightly inferred that the obligation is grave, although, as is obvious, there may be plausible reasons allowing them to wear other clothing, such as persecution or travel in regions where different customs prevail.
Article 498 of the Italian Penal Code substantially reproduces (though, according to the prevailing interpretation, extending it even to non-Catholic churches) the provision
that forbids the wearing of the ecclesiastical habit outside churches and religious buildings, and consequently also in private; finally, the offender may seek sacramental absolution for his sin from any confessor (can. 2314, § 2). In the second case: a) if the convert has certainly received an invalid baptism, no abjuration is required; it suffices to administer baptism; b) if the baptism is certainly valid, the following procedure is followed: abjuration, absolution from the censure in the external forum, sacramental confession; c) if the baptism is doubtful, the procedure is: abjuration, conditional baptism, sacramental confession, conditional absolution.
2. CEREMONIES AND FORMULA OF THE ABJURATION — The abjuration may be received only from the local Ordinary (excluding the vicar general without special mandate) or from a delegate appointed for the case, and must be made in the presence of at least two witnesses (can. 2314, § 2). The rite to be followed, the formalities and precautions are set out in the Roman Pontifical (Part III, title: Ordo ad reconciliandum apostatam, schismaticum vel haereticum) and in certain documents of the Holy Office, including those of 20 July 1859, 28 March 1900, and 19 February 1916. The phrase “to the use of the services of exchange of food and goods” in the cited can. 2314, § 2 refers to these formalities and precautions. Some formulas were approved by the Holy Office in 1925, 1933, and 1936 respectively for dissidents (especially Russians) and for Protestants. The local Ordinary, moreover, remains free to prescribe an even shorter formula.
Formulas of abjuration are also found for unbelievers (pagans, Jews, Muslims) (cf. Rituale Romanum, title II, chap. IV: Ordo baptismi adultorum), but evidently these are not abjurations in the proper sense.