Can Cousins Marry in the Church?

Q: Can cousins get married in the Church? I don’t want to marry my cousin, I’m just wondering!  –Jeremy

A: When it comes to the biological relationship between prospective spouses, the Church has laws which are based on natural law. We all know that genetic problems tend to arise in children whose parents are too closely related by blood. Canon law is therefore simply reflecting what nature (i.e., God) intended.

A casual reader of canon 1091, the canon which directly addresses Jeremy’s question, will most likely find it hopelessly confusing. Among other things, it states that marriage is invalid between persons related by consanguinity in all degrees of the direct line (c. 1091.1), and that in the collateral line, marriage is invalid up to and including the fourth degree (c. 1091.2). Understanding how to apply these abstract rules to concrete cases probably requires a little unpacking first!

To begin with, it would be helpful to clarify some terms. “Consanguinity” refers only to biological, blood relationships (and not to relationships created through marriage, such as that between a mother-in-law and her son-in-law).  The “direct line” refers to direct descendants—parents, grandparents, children and grandchildren. Knowledge of the meanings of these two terms should help us now to understand canon 1091.1: marriage is always invalid between parent and child, grandparent and grandchild, great-grandparent and great-grandchild, etc. This should certainly be no surprise to anyone, because we are quite comfortable with the notion, founded in natural law, that such marriages are forbidden. (Natural law is, incidentally, the rationale behind the fact that these marriages are against the civil law as well.)

While direct-line consanguinity is pretty easy to calculate, figuring other blood relationships can quickly become rather complex. The term “collateral line” refers to all relationships that at least partly involve siblings. Brothers and sisters are the clearest example of relatives in the collateral line, but collateral-line consanguinity refers also to relations between aunt/uncle and niece/nephew—as well as to cousins.

Complications arise because as we all know, there are various types of aunt/uncle and niece/nephew relationships (great-aunt and great-nephew is one example), and there are certainly many types of cousins. What we popularly term “first cousins,” for example, are the children of two siblings, but there are second- and third-cousins to contend with as well. The list of collateral relationships goes on and on!

To make the picture even more confusing, the Code of Canon Law is based on old Roman law when it comes to family relationships, so it doesn’t use our common terminology. That’s why the term “first cousin,” for example, is found nowhere in the code. In canon 108, the code provides some general definitions to explain the system it does use, which involves lines and degrees.

We’ve already seen how the “lines” work; consanguinity involves either direct lines or collateral lines. But how does one calculate the “degrees”? Let’s take a few cases as examples, to see how it works, and then see how canon 1091 on marriage directly applies to them.

Picture two siblings, Nancy and Mark. They are two people with a common ancestor (or in this case, two common ancestors—their parents). In accord with canon 108.3, we count the persons in both lines, but not the common ancestor(s). There are only two people involved here, and therefore Nancy and Mark’s relationship is considered second-degree consanguinity in the collateral line.

Can Nancy and Mark marry validly in the Church? Obviously not, because canon 1091.2 states that marriage in the collateral line is invalid up to the fourth degree, and their relationship is much closer than that.

Now imagine Uncle Bill and his niece Susan. Let’s say that Susan’s mother Mary is the sister of Uncle Bill. In this case, their “common ancestor” would be the parent(s) of Bill and Mary. In accord with the same canon 108.3, we count all persons involved in this relationship, except for the common ancestor: Susan, Bill, and Mary add up to three. Thus we can say that uncle and niece are related in the third degree of the collateral line.

Can Bill and Susan marry in the Catholic Church? Again, canon 1091.2 gives us the answer: any marriage in the collateral line up to the fourth degree is invalid. Since Bill and Susan are related in the third degree, they cannot marry validly.

This brings us now to the relationship addressed in Jeremy’s question: what is the degree of consanguinity between two cousins? Well, let’s imagine Cousin Jenny and Cousin Mike. Jenny’s mother, Beth, is the sister of Mike’s father, David. The common ancestor(s) in this case is the parent(s) of Beth and David. If we count all the persons involved in this relationship, minus the common ancestor, we find four persons involved. So these two cousins—who in our parlance are “first cousins”—are related in the fourth degree of the collateral line.

So can Cousin Jenny validly marry Cousin Mike? Not according to canon 1091.2, which says marriages are invalid up to and including the fourth degree. First cousins, therefore, cannot marry in the Church.

As for second, third, and other cousins, however, their degree of consanguinity is farther removed—they are related in the fifth, sixth, and even further degrees of the collateral line. According to canon 1091, therefore, these cousins can get married in the Catholic Church.

If readers’ heads are spinning by this point, there’s no shame in feeling confused—because it is confusing! And unfortunately, there’s one more added twist to complicate things even further.

We saw in “Could the Pope Change the Law to Allow Women Priests?” that some of the Church’s laws are held to be divine laws, while others are “merely” ecclesiastical laws. The latter have been established by human authority, but the former were instituted by God Himself. The Church holds that if a law was made by church authorities, it can be dispensed if there is sufficient justification for doing so. (We looked at the whole concept of dispensation back in “Marriage Between a Catholic and a Non-Catholic.”) In contrast, church laws which are believed to stem directly from a divine command, or are otherwise reflections of natural law, can never be dispensed in any case.

It shouldn’t be difficult to appreciate why church authorities will never grant a dispensation that permits a father to marry his daughter, or a sister to marry her brother. These relationships are so close that such a marriage would be considered a violation of natural law—and thus contrary to what God has intended.

But as for two first cousins… the Church’s position is that they are forbidden to marry only by ecclesiastical law, not by divine law. For this reason it is canonically possible to receive a dispensation that permits two first-cousins to marry validly in the Catholic Church.  (This assumes, of course, that it is legal under civil law in the area where the marriage is to take place—and in the U.S., some states permit it, while others don’t.)

History buffs are undoubtedly well aware of countless examples of such dispensations granted to members of European royal families in centuries past. Often it was argued—convincingly—that it was politically expedient for the two cousins to marry, because their wedding would contribute to peaceful relations between their two countries. Sadly, the bloodlines of most royal houses became so intertwined that significant genetic problems eventually arose among some family members. The daughter of Spain’s Ferdinand and Isabella, for example, was apparently insane and became known as “Juana la Loca,” or “Joan the Mad.” And just a couple of generations later, Carlos, the eldest son of Spain’s King Phillip II, was born physically handicapped and mentally unstable. It is commonly understood that too much intermarriage between too many cousins wreaked genetic havoc within Europe’s royal families, leading to the various medical problems suffered by these and numerous other royals.

Fortunately, the ostensible political need for repeated dispensations permitting such marriages is a thing of the past. While a diocesan bishop may certainly grant a dispensation allowing two first-cousins to marry, rest assured that he will take a closer look at any other relations between the two families’ bloodlines first.  The Church will always watch out for the best interests of the faithful, which in some cases may involve allowing two first-cousins to marry. But in general, we can see here a good instance of canon law working hand-in-hand with natural law—which, after all, was established by God Himself.

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