The Canon Law Made Easy site has an interesting discussion of the difference between an impediment and an irregularity when it comes to the receiving of Holy Orders. An impediment is not permanent.
An impediment is something that prevents Holy Orders but is not necessarily permanent. For instance, a married man can not be a priest. But if his wife dies, the irregularity is removed.
Canon 1041 lists the irregularities:
Can. 1041 The following are irregular for receiving orders:
1/ a person who labors under some form of amentia or other psychic illness due to which, after experts have been consulted, he is judged unqualified to fulfill the ministry properly;
2/ a person who has committed the delict of apostasy, heresy, or schism;
3/ a person who has attempted marriage, even only civilly, while either impeded personally from entering marriage by a matrimonial bond, sacred orders, or a public perpetual vow of chastity, or with a woman bound by a valid marriage or restricted by the same type of vow;
4/ a person who has committed voluntary homicide or procured a completed abortion and all those who positively cooperated in either;
5/ a person who has mutilated himself or another gravely and maliciously or who has attempted suicide;
6/ a person who has placed an act of orders reserved to those in the order of episcopate or presbyterate while either lacking that order or prohibited from its exercise by some declared or imposed canonical penalty.
I guess the moral of the story is if you make a public vow of chastity, don't even try becoming a priest.
|Canon 1041 - 2|
|Canon 1041 - 3|
|Canon 1041 - 4|