§ 9. Natural Relationship or Consanguinity

Preliminary Note. A threefold relationship is commonly distinguished: 1. natural, which is also called consanguinity or kinship; 2. spiritual, which arises from baptism and confirmation; 3. legal, which proceeds from legal adoption. Each must be treated separately.

831. Notion. The impediment of consanguinity (unity of blood) is the proximity of persons descending from the same proximate stock or progenitor, which invalidates matrimony within determined degrees.

Explanation. The foundation of consanguinity is a common and indeed proximate stock, from which the persons about to marry descend through carnal generation. All men indeed descend from the same first stock, namely, from Adam, but matrimony is prohibited only between persons who descend from a proximate stock within the third generation. For judging correctly concerning consanguinity insofar as it is an impediment of matrimony, three things must be considered especially: the stock, the line, and the degree.

The stock (root, trunk) is called that person (whether male or female) from whom, as from a common root, the persons about to marry (whose consanguinity is in question) descend through carnal generation (whether legitimate or illegitimate, whether mediate or immediate). Hence, for example, a grandfather is the common stock of grandchildren, a father of children, etc.

A line is called the natural series of consanguineous persons. A twofold line is distinguished: direct and collateral. A direct line is called a series of persons, one of whom descends from another, and therefore it comprises: a) ascendants, such as father, grandfather, great-grandfather (the direct ascending line); b) descendants, such as son, grandson, great-grandson (the direct descending line). - A collateral (transverse, oblique) line is a series of persons who indeed descend from one and the same stock, but not one from another; for example, brother and sister indeed descend from the same stock, namely, from the father, but the brother does not descend from the sister, and conversely the sister does not descend from the brother. If persons of the collateral line are equally distant from the common stock, as a brother and sister from their father or grandchildren from their grandfather, there is an equal collateral line; but if one person is farther from the common stock than another, for example, a brother and a female cousin, there is an unequal collateral line. (See below the tree of consanguinity.)

A degree is the measure of distance in consanguinity. Two principal methods exist for computing these degrees or this distance: the civil or Roman computation, which is commonly in force in civil laws and in the Eastern Church;¹⁸⁰ and the canonical (Germanic, Teutonic) computation, which is now in force in the Latin Church.¹⁸¹ In the direct line both computations are the same. But in the collateral line the civil computation counts the degrees or generations both on the bridegroom's side and on the bride's side, so that as many degrees are judged to be present as there are generations from both sides taken together. For example, a brother and sister are consanguineous in the second degree according to the civil computation, because there is one generation from the common stock (the father) on the brother's side, and likewise there is one generation on the sister's side. - The canonical computation, however, indeed counts the degrees or generations from each person about to marry up to the common stock, but does not join them together. Thus, for example, a brother and sister according to this computation are consanguineous in the first degree, because from both the brother and the sister to the common stock there is only one generation. - With these things premised, the following rules are given by the Code of Canon Law, can. 96, for computing degrees.

Figure 1. Tree of Consanguinity

                              Great-grandfather / Great-grandmother (3)
                    __________________________|__________________________
                   /                          |                          \
 Great paternal uncle / aunt (3)     Grandfather / Grandmother (2)     Great maternal uncle / aunt (3)
             |                    ___________|___________                    |
       Their children (3)        /           |           \             Their children (3)
                         Paternal uncle / aunt (2)  Father / Mother (1)  Maternal uncle / aunt (2)
                                  |           |           |
                    Their children (3)   Brother (1)  N  Sister (1)   Their children (3)
                                  |                       |
                           Their children (2)      Their children (2)
                                  |                       |
                          Brother's children (3)   Sister's children (3)

                                         N
                                         |
                                   Son / Daughter (1)
                                         |
                              Grandson / Granddaughter (2)
                                         |
                         Great-grandson / Great-granddaughter (3)

Rule 1. In the direct line there are as many degrees as there are generations; or, what is the same: there are as many degrees as there are persons, the stock being subtracted.

For example, between a bridegroom and his great-grandfather there are three degrees, because there are three generations, or three persons if the great-grandfather is subtracted.

Rule 2. In an equal collateral line there are as many degrees as there are generations (or persons, the stock being subtracted) computed on one side only (whether it is the bridegroom or the bride).

For example, first cousins are consanguineous in the second degree, because there are two generations up to the common stock, who is the grandfather. There are also two persons, if the grandfather is subtracted, namely, the first cousins themselves and their parents.

Names of Blood Relatives in Certain Vernacular Languages

Direct Line

Collateral Line

Rule 3. In an unequal collateral line there are as many degrees as there are generations (or persons, the stock being subtracted) to be computed in the longer line.

For the adage is valid: the more remote degree draws the nearer to itself. Thus, for example, a paternal uncle and niece,¹⁸² that is, a brother's daughter, are consanguineous in the second unequal collateral degree; for the common stock is the grandfather, from whom the paternal uncle is distant by one degree, but the niece by two degrees. In petitions for dispensations both degrees must be expressed; this is commonly done in this manner: a paternal uncle and niece are consanguineous in the second degree touching the first. For finding and computing degrees more easily, the so-called "tree of consanguinity" was already delineated in the Corpus of Canon Law,¹⁸³ whose figure, slightly altered, we have given above, as also the names of blood relatives in certain vernacular languages.

¹⁸⁰ Papp-Szilagyi, Enchir. iur. eccl. orient. cath., 262.

¹⁸¹ c. 2, C. 35, q. 5.

¹⁸² Onkel und Nichte [uncle and niece].

¹⁸³ After c. 6, C. 35, q. 5.

832. Divisions. Consanguinity is distinguished:

a) as legitimate and illegitimate, according as generation was effected in a valid or putative matrimony, or outside matrimony. Illegitimate offspring, however, can be legitimated, as will be said below, n. 884;

b) as full (perfect) and less full (imperfect), according as consanguineous persons descend from the same two parents, or only from the same father or the same mother. - Brothers having the same father but not the same mother are called "consanguineous"; but those having the same mother but not the same father are called "uterine"; while those having the same father and the same mother are called "germane";

c) as cognation and agnation, according as consanguinity arose through the female line or mother, or through the male line¹⁸⁴ or father;

d) as simple and multiple, according as two consanguineous persons descend from one common stock, or according as several common stocks are present. Thus according to the discipline now in force.¹⁸⁵ Formerly other cases of multiple consanguinity also occurred.

Since in practice it is sometimes sufficiently difficult to discover multiple consanguinity, it is necessary to explain at somewhat greater length at least two cases of multiple consanguinity.

¹⁸⁴ In the old German law, cognates were called Spillmagen and agnates Schwertmagen.

¹⁸⁵ Code of Canon Law, can. 1076, § 2.

833. Multiple consanguinity. First case: if among the ascendants of two spouses members of one family celebrated marriages with members of another family, for example, two brothers of one family married two sisters of another family. In this case there are two common stocks, as is apparent from the diagram placed here. For both grandfathers of the bridegroom and both grandfathers of the bride were brothers and sisters. Hence the two persons about to marry are consanguineous in a double third degree. As is evident of itself, other similar examples can also be devised.

Figure 2. First case

Common stock                         Common stock
     |                                    |
brother ─ sister                    brother ─ sister
  |          |                        |          |
 ...        ...                      ...        ...
  |          |                        |          |
Bridegroom  Bride                  Bridegroom  Bride

Second case: if the ascendants were consanguineous and one of them successively married two consanguineous women, as is clearly seen from the diagram placed above (fig. 3). In this case there are likewise two common stocks, and the persons about to marry are consanguineous in the third and second degree.

Figure 3. Second case

Common stock
     |
consanguineous ascendants
     |
successive unions with two consanguineous women
     |
Bridegroom                         Bride

834. Note. When a dispensation from the impediment of consanguinity is to be requested, it must necessarily be expressed whether the consanguinity is simple or multiple; whether it is full or half-full; whether it is in the direct or in the collateral line. It is highly expedient that a diagram of consanguinity be drawn in the petition, as is shown here; indeed, in some dioceses a diagram of this kind is expressly required in every petition submitted.

Figure 4. Diagram of Consanguinity

Simon Schmitz
├── Andrew Schmitz
│   └── Paul Schmitz + Anna Meyer
│       └── Petrus Schmitz, bridegroom
└── Clara Schmitz
    └── Paul Müller + Clara Schneider
        └── Anna Müller, bride

Method of finding the degree of consanguinity. Several methods are available, of which, however, the following seems easier, clearer, and safer. If any reasonable doubt arises for the parish priest concerning the consanguinity of those about to marry, the names of the bridegroom and bride are to be written on a sheet of no very small size; then above the bridegroom's name all the names of his ascendants, and similarly above the bride's name all the names of her ascendants. Afterward the intervening generations are to be counted until the common stock is reached. The number of these generations from the common stock to the bridegroom gives the degrees of consanguinity on his side; but the number of generations from the common stock to the bride gives the degrees of consanguinity on the bride's side. If, for example, three generations are found from the common stock both on the bridegroom's side and on the bride's side, there is consanguinity in the equal third degree of the collateral line. See the diagram placed above (fig. 4). But if there are four generations from the common stock to the bridegroom and three to the bride, then the persons about to marry are consanguineous in the fourth degree of the collateral line touching the third. In this last case a dispensation is no longer necessary, because according to the adage stated above, the more remote degree draws the nearer degree to itself, and a dispensation is required only, as will be said below, if the persons about to marry are consanguineous up to and including the third degree. If multiple consanguinity is present, the degrees must be computed from each common stock, or according to the diverse paths by which ascent is made to each common stock.

835. Origin of the impediment of consanguinity.

1. From natural law itself arises the diriment impediment of consanguinity in the direct line (whether ascending or descending), and it extends not only to the first degree (between father and daughter, between mother and son), but also to all other degrees. In the first degree of the direct line, that is, between father and daughter as also between mother and son, all admit that matrimony is prohibited by natural law itself, and even barbarous peoples themselves, indeed even brute animals, are wont to recoil from a carnal union of this kind. The reason is taken both from the physical and from the moral order. For from such carnal intercourse either no offspring or weak and deformed offspring is wont to be born. Moreover, in marital and carnal union there exists equality between the contracting parties, whereas between parents and children there is not equality, but subjection and reverence due to parents. - In other degrees of the direct line matrimony is probably also prohibited by natural law because of the same reasons of physical and moral order; but several very weighty authors, such as Billuart,¹⁸⁶ Cajetan,¹⁸⁷ to whom St. Thomas¹⁸⁸ seems to favor, teach that consanguinity in the other degrees dirimes matrimony by ecclesiastical law alone. Hence, in practice, if a case should occur in which a grandfather in paganism had married his granddaughter and afterward one or the other spouse were baptized, the Holy See would have to be consulted about what must be done.

2. By ecclesiastical law alone the diriment impediment of consanguinity in all degrees of the collateral line arose in the New Testament. Thus the more probable opinion, concerning which Benedict XIV says: "There is no agreement among theologians whether matrimony between brother and sister is prohibited by natural, divine, or human law; certainly St. Thomas, Gonzalez, Pontius, Parisius, and Aversa acknowledge only a prohibition of positive law."¹⁸⁹ - The reason is that between a brother and sister, or other blood relatives of remoter degrees, there does not intervene such a relation of reverence and subjection as exists between parents and children. Then it is incongruous to say that immediately at the beginning of the world God established something contrary to natural law itself. But it is certain that the sons of Adam took their own germane sisters as wives. From this opinion it follows that, if in paganism a brother and sister contracted matrimony (provided the civil law of that region did not invalidate such a matrimony), and if afterward one or both spouses are baptized, their matrimony cannot by that very fact be declared invalid, but recourse must be had to the Holy See. - If it is a question of a matrimony to be contracted, the Supreme Pontiff never dispenses so that matrimony may be entered between brother and sister, or in the first degree of the collateral line, even if that consanguinity is not certain but only doubtful;¹⁹⁰ but he very rarely dispenses in the second degree touching the first, for example, so that a maternal uncle may marry his sister's daughter.^190a

¹⁸⁶ De matrim., diss. 7, a. 4, § 2, I say 3°.

¹⁸⁷ Comm. in 2, 2, q. 154, a. 9.

¹⁸⁸ The Angelic Doctor says: "In the intercourse of related persons there is something which is in itself indecent and repugnant to natural reason, as that intercourse should occur between parents and children, whose relationship is of itself and immediate; for children naturally owe honor to parents. Hence the Philosopher says that a certain horse, because it had been deceived so that it coupled with its mother, cast itself down as though from horror, because even in some animals a natural reverence toward parents is present. - But other persons, who are not joined according to themselves but by order to parents, do not have such indecency from themselves; rather, decency or indecency in this matter varies according to custom and human and divine law, because the use of venereal things, which is ordained to the common good, is subject to law. And therefore, as Augustine says: 'Intercourse between sisters and brothers, the more ancient it was under the compulsion of necessity, the more afterward it was made damnable when religion prohibited it'" (S. theol. 2, 2, q. 154, a. 9, ad 3). Similar things are found in Suppl., q. 54, a. 3. Certain older authors wittily refuted the opposite opinion, saying: If consanguinity in all degrees of the direct line dirimed matrimony by natural law itself, Adam, restored to life, could marry no woman, because all descended from him in the direct line.

¹⁸⁹ Benedict XIV, Epistle Aestas anni, n. XIII, October 11, 1757. Wernz-Vidal, Ius matr., n. 348, note 60 ff., strongly maintains that the impediment of consanguinity in the first degree of the collateral line arose from natural law. Several others, such as Sanchez, Suarez, Lugo, Noldin, etc., teach the same.

¹⁹⁰ Benedict XIV, loc. cit.; and Code of Canon Law, can. 1076, § 3.

^190a Instruction of the Sacred Congregation of the Sacraments, August 1, 1931 (Acta Apost. Sed. XXIII, 413).

836. Extent of the impediment of consanguinity. According to the discipline now in force in the Latin Church, consanguinity in the collateral line dirimes matrimony up to and including the third degree; and it makes no difference whether the consanguinity arose from a legitimate or an illegitimate bed.¹⁹¹

Formerly the impediment of consanguinity in the collateral line extended to the seventh degree and, after the Fourth Lateran Council, to the fourth degree; but now, after May 19, 1918, it is restricted to the third degree. - Since, according to the adage cited repeatedly, the more remote degree draws the nearer to itself, the diriment impediment of consanguinity is no longer present if on one side of the contracting parties there are four degrees up to the common stock, although on the other side there are only two or three degrees. - The best rule to be given to the people and sufficiently easy to apply in practice for discerning whether the impediment of consanguinity is present is this:

The impediment of consanguinity is not present if the parents of those about to marry were not at least first cousins, or, what is the same: if the grandparents of those about to marry were not brothers or sisters.

¹⁹¹ Code of Canon Law, can. 1076, § 2. In the Eastern Church this impediment is valid up to the seventh degree, that is, up to the third degree according to the canonical computation. Cf. Papp-Szilagyi, loc. cit., § 107.

837. The suitability of the impediment of consanguinity is evident especially from a threefold reason:

1. The social good is greatly promoted through it. As St. Augustine bears witness,¹⁹² it is necessary that the whole human race, by the will of God and by bonds of charity extended more and more widely, grow together into one society and the city of God. But marriages, as seedbeds of charity, are means most suitable and efficacious for effecting this union, provided, however, that they are duly entered and holily preserved. But if marriages were contracted only among blood relatives, this social union would be obtained less perfectly.¹⁹³

2. The moral good is preserved through it. Blood relatives are wont to live together with familiar intercourse, often dwell under the same roof, and visit one another rather frequently. From this familiar intercourse great dangers to chastity could very easily arise if blood relatives were not conscious from earliest childhood that they could never enter legitimate nuptials with one another. Therefore, the impediment of consanguinity is a strong guardian of morality.

3. The physical good of the offspring is better obtained. For experience proves that offspring born from the matrimony of blood relatives are often weak both in mind and in body.¹⁹⁴ Certainly, if both spouses, free from every bodily defect, enjoy robust health, a danger of this kind for the offspring is sometimes absent, but this case does not always occur. Generally it is permissible to affirm that offspring born from the matrimony of blood relatives are of an inferior condition to the offspring of other marriages (other things being equal). - Since these things are so, confessors and parish priests should deter the faithful from entering marriages between blood relatives.

¹⁹² De civ. Dei, bk. 15, c. 16 (c. un., C. 35, q. 1).

¹⁹³ Cf. St. Thomas, Suppl., q. 54, a. 4.

¹⁹⁴ Hence that adage: Heirat im Blut tut selten gut [marriage within the blood seldom turns out well].

838. Cessation of this impediment. This impediment ceases only through a dispensation of the Supreme Pontiff, which, however, is never granted not only in consanguinity of the direct line, as probably diriming matrimony by natural law in all degrees, but also in the first degree of the collateral line, as was said. Therefore, not even in danger of death can a parish priest or confessor permit matrimony between a brother and sister.