[This is according to the Catholic Tradition]
Impediments to marriage
326. For marriage to be valid, it is necessary that the contracting parties not be bound by any of the impediments that annul it, and that they observe the laws of the Church.
The one who contracts marriage must be free from all impediments.
There are impediments that are impedientes [no translation found] and dirimentes [no translation found].
The impedientes make the marriage illicit, but not invalid; the dirimentes make it illicit and invalid.
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Impedientes impediments
There are three impedientes impediments:
1. The simple vow of virginity, of perfect chastity, of not marrying, of receiving Holy Orders, and of embracing the religious state.
2º Legal kinship, arised of adoption, is an impediment in those regions where it is so by civil law.
3º Mixed religion: The Church forbids marriage between two baptized persons, one of whom is Catholic and the other is adhered to a heretical or schismatic sect.
It is forbidden, even by divine right, if there is a danger of perversion of the catholic married spouse or of the offspring.
Dispensation from the impediments of ecclesiastical law can be obtained if there is a just cause.
For the dispensation from the impediment of mixed religion, the following is required:
1. That just and serious causes arise.
2. That the non-Catholic party give a formal promise to avoid any danger that the Catholic spouse will abandon the Catholic religion, or that he or she will not practice it, and that both spouses promise to have all children of both sexes baptized and educated Catholicly.
Neither before nor after marriage may they present themselves to the non-Catholic minister, in his capacity as such, to give or renew the matrimonial consent.
The faithful should beware of marrying people who have notoriously left the Catholic faith, even if they have not passed into a heretical or schismatic sect, or who belong to societies condemned by the Church such as Freemasons, Socialists, Communists, Anarchists, etc.
In order for marriage to take place with such persons, there must be serious causes, and the same precautions must be taken as in the case of mixed religion.
What should the bride do, if the groom tells her that, after they are married, he will not allow her to go to Mass or fulfill any other religious duty?
In this case, she must resolutely declare to him that she desists from contracting marriage, if he does not give her a formal promise that he will leave her at complete liberty to comply with all that the holy religion prescribes. [And I counsel that the promise must be before two witnesses that tell about it to all the family]
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Dirimentes Impediments
1. Error about persons, not about their qualities.
2. Servile condition (being a slave, the other party ignoring it)
3. The solemn vow of chastity, taken in a religious order; the simple, when by pontifical prescription it has the force of annulling the marriage.
4. Kinship. It is threefold: natural, spiritual and legal.
Natural kinship or consanguinity is an impediment: in a straight line, always; in the collateral line, up to and including the third degree
In the collateral line, the first degree is between siblings, the second is between first cousins and the third between second cousins.
Spiritual kinship is an impediment only by Baptism.
It is contracted by the baptized person with whom he baptizes and the godparents.
Legal kinship. It arises from the adoption made in a legal manner, that is, with the intervention of the competent judge.
It is a diriment impediment only in the regions where it is so by civil law.
5. Crime. The following contract this impediment:
a) Those who committed adultery among themselves, with a mutual promise of marriage, or attempted to contract it even by the sole civil act, if the adultery and the mutual promise of marriage took place during the same legitimate marriage.
b) Those who, during the same legitimate marriage, committed adultery among themselves, and one of the two killed the spouse.
6. Disparity of worship. Between a person who is not baptized and another who is baptized in the Catholic Church, or who has converted to a church of schism or heresy.
7. Force or grave unjust fear by an external and free cause, if in order to get rid of it one is forced to marry.
8. Order. Only the major Orders.
9. To be bound in marriage.
10. Public honesty. It arises from every invalid marriage and from public and notorious concubinage.
It nullifies marriage in the 1st and 2nd degrees, in a straight line, between the man and the woman's blood relatives and between the woman and the man's blood relatives.
11. Not being of the right age. The woman must be fourteen years old and the male sixteen.
12. Affinity. The relationship that one spouse has with the blood relatives of the other.
Affinity is born of every valid marriage.
It makes marriage null and void: in a straight line, to any degree; in the collateral line, up to and including the second.
13. Clandestinity. For the marriage to be valid, it must take place in the presence of the parish priest, or the local Ordinary, or a priest delegated by one of the two, and the witnesses.
When the presence of the parish priest, ordinary or delegated priest cannot be obtained without serious inconvenience (such as a long distance or other cause), the marriage is valid and licit in the presence of only two witnesses:
a) If either of the contracting parties is in danger of death.
b) Even outside this danger, when it is prudently foreseen that this state of affairs will last one month.
If another unauthorized priest is easily found, who may be present, he should be called and attend the marriage, along with the witnesses; but the marriage will be valid with the witnesses only, even if the priest does not attend, nor is he invited.
The priest, or otherwise the witnesses, together with the contracting parties, are obliged to see that the marriage that has taken place is recorded as soon as possible in the prescribed books.
14. Impotence to fulfill the conjugal duty. For it to be an impediment, it must precede the marriage and there must be no hope that it will cease.
15. Abduction. It is an impediment between the abductor and the woman, who has suffered the violent abduction with the aim of marriage.
The impediment ceases if the woman has been separated from the abductor and placed in a safe and free place. [This book was written before 1973, when Stockholm syndrome was discovered. I don't know if the Church reviewed this point.]
There is also an impediment when the man, with a view to marriage, violently detains the woman in her home, or in the place to which she herself freely went.
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Waiver of impediments
Impediments have their origin: some in natural law, others in divine law, and others in ecclesiastical law.
All have the good of the family and society as their goal.
Impediments of ecclesiastical law may be dispensed with by the pope, or by the one who has received his delegation.
It is very convenient that, when the impediment is noticed, the marriage should be desisted from, and dispensations should not be resorted to, unless serious causes compel it.
The Church grants dispensations only for just causes and to avoid greater evils.
The faithful are obliged to manifest to the ecclesiastical authority the impediments to marriage of which they are aware; for this reason the parish priests publish the admonitions or proclamations.
Only the Church has the power to place impediments, to judge the validity of marriage and to waive the impediments that she has placed; because Christian marriage is a Sacrament.
Jesus Christ conferred the right to legislate and decide on sacred things to the Church alone.
The civil authority can legislate only regarding the civil effects of marriage, such as inheritances, wills, etc.