Of the Impediment of Consanguinity

Of the Impediment of Consanguinity — St. Thomas Aquinas asks: Whether consanguinity is rightly defined?; Whether consanguinity is fittingly distinguished by degrees and lines?; Whether consanguinity is an impediment to marriage by virtue of the natural law?; Whether the degrees of consanguinity that are an impediment to marriage could be fixed by the Church?.

We must next consider the impediment of consanguinity. Under this head there are four points of inquiry:

Article 1: Whether consanguinity is rightly defined?

According to the Philosopher (Ethic. iii, 11, 12) "all friendship is based on some kind of fellowship." And since friendship is a knot or union, it follows that the fellowship which is the cause of friendship is called "a tie." Wherefore in respect of any kind of a fellowship certain persons are denominated as though they were tied together: thus we speak of fellow-citizens who are connected by a common political life, of fellow-soldiers who are connected by the common business of soldiering, and in the same way those who are connected by the fellowship of nature are said to be tied by blood [consanguinei]. Hence in the above definition "tie" is included as being the genus of consanguinity; the "persons descending from the same common ancestor," who are thus tied together are the subject of this tie. while "carnal procreation" is mentioned as being its origin.

Article 2: Whether consanguinity is fittingly distinguished by degrees and lines?

Consanguinity as stated () is a certain propinquity based on the natural communication by the act of procreation whereby nature is propagated. Wherefore according to the Philosopher (Ethic. viii, 12) this communication is threefold. one corresponds to the relationship between cause and effect, and this is the consanguinity of father to son, wherefore he says that "parents love their children as being a part of themselves." Another corresponds to the relation of effect to cause, and this is the consanguinity of son to father, wherefore he says that "children love their parents as being themselves something which owes its existence to them." The third corresponds to the mutual relation between things that come from the same cause, as brothers, "who are born of the same parents," as he again says (Ethic. viii, 12). And since the movement of a point makes a line, and since a father by procreation may be said to descend to his son, hence it is that corresponding to these three relationships there are three lines of consanguinity, namely the "descending" line corresponding to the first relationship, the "ascending" line corresponding to the second, and the "collateral" line corresponding to the third. Since however the movement of propagation does not rest in one term but continues beyond, the result is that one can point to the father's father and to the son's son, and so on, and according to the various steps we take we find various degrees in one line. And seeing that the degrees of a thing are parts of that thing, there cannot be degrees of propinquity where there is no propinquity. Consequently identity and too great a distance do away with degrees of consanguinity; since no man is kin to himself any more than he is like himself: for which reason there is no degree of consanguinity where there is but one person, but only when one person is compared to another.

Nevertheless there are different ways of counting the degrees in various lines. For the degree of consanguinity in the ascending and descending line is contracted from the fact that one of the parties whose consanguinity is in question, is descended from the other. Wherefore according to the canonical as well as the legal reckoning, the person who occupies the first place, whether in the ascending or in the descending line, is distant from a certain one, say Peter, in the first degree---for instance father and son; while the one who occupies the second place in either direction is distant in the second degree, for instance grandfather, grandson and so on. But the consanguinity that exists between persons who are in collateral lines is contracted not through one being descended from the other, but through both being descended from one: wherefore the degrees of consanguinity in this line must be reckoned in relation to the one principle whence it arises. Here, however, the canonical and legal reckonings differ: for the legal reckoning takes into account the descent from the common stock on both sides, whereas the canonical reckoning takes into account only one, that namely on which the greater number of degrees are found. Hence according to the legal reckoning brother and sister, or two brothers, are related in the second degree, because each is separated from the common stock by one degree; and in like manner the children of two brothers are distant from one another in the fourth degree. But according to the canonical reckoning, two brothers are related in the first degree, since neither is distant more than one degree from the common stock: but the children of one brother are distant in the second degree from the other brother, because they are at that distance from the common stock. Hence, according to the canonical reckoning, by whatever degree a person is distant from some higher degree, by so much and never by less is he distant from each person descending from that degree, because "the cause of a thing being so is yet more so." Wherefore although the other descendants from the common stock be related to some person on account of his being descended from the common stock, these descendants of the other branch cannot be more nearly related to him than he is to the common stock. Sometimes, however, a person is more distantly related to a descendant from the common stock, than he himself is to the common stock, because this other person may be more distantly related to the common stock than he is: and consanguinity must be reckoned according to the more distant degree.

Article 3: Whether consanguinity is an impediment to marriage by virtue of the natural law?

According to the natural law whatever is an obstacle to the good of the offspring is an impediment to marriage. Now consanguinity hinders the good of the offspring, because in the words of Gregory (Regist., epis. xxxi) quoted in the text (Sent. iv, D, 40): "We have learnt by experience that the children of such a union cannot thrive." Therefore according to the law of nature consanguinity is an impediment to matrimony.

Further, that which belongs to human nature when it was first created is of natural law. Now it belonged to human nature from when it was first created that one should be debarred from marrying one's father or mother: in proof of which it was said (Gn. 2:24): "Wherefore a man shall leave father and mother": which cannot be understood of cohabitation, and consequently must refer to the union of marriage. Therefore consanguinity is an impediment to marriage according to the natural law.

In relation to marriage a thing is said to be contrary to the natural law if it prevents marriage from reaching the end for which it was instituted. Now the essential and primary end of marriage is the good of the offspring. and this is hindered by a certain consanguinity, namely that which is between father and daughter, or son and mother. It is not that the good of the offspring is utterly destroyed, since a daughter can have a child of her father's semen and with the father rear and teach that child in which things the good of the offspring consists, but that it is not effected in a becoming way. For it is out of order that a daughter be mated to her father in marriage for the purpose of begetting and rearing children, since in all things she ought to be subject to her father as proceeding from him. Hence by natural law a father and mother are debarred from marrying their children; and the mother still more than the father, since it is more derogatory to the reverence due to parents if the son marry his mother than if the father marry his daughter; since the wife should be to a certain extent subject to her husband. The secondary essential end of marriage is the curbing of concupiscence; and this end would be forfeit if a man could marry any blood-relation, since a wide scope would be afforded to concupiscence if those who have to live together in the same house were not forbidden to be mated in the flesh. Wherefore the Divine law debars from marriage not only father and mother, but also other kinsfolk who have to live in close intimacy with one another and ought to safeguard one another's modesty. The Divine law assigns this reason (Lev. 18:10): "Thou shalt not uncover the nakedness" of such and such a one, "because it is thy own nakedness."

But the accidental end of marriage is the binding together of mankind and the extension of friendship: for a husband regards his wife's kindred as his own. Hence it would be prejudicial to this extension of friendship if a man could take a woman of his kindred to wife since no new friendship would accrue to anyone from such a marriage. Wherefore, according to human law and the ordinances of the Church, several degrees of consanguinity are debarred from marriage.

Accordingly it is clear from what has been said that consanguinity is by natural law an impediment to marriage in regard to certain persons, by Divine law in respect of some, and by human law in respect of others.

Article 4: Whether the degrees of consanguinity that are an impediment to marriage could be fixed by the Church?

Our Lord said to His disciples (Lk. 10:16): "He that heareth you heareth Me." Therefore a commandment of the Church has the same force as a commandment of God. Now the Church sometimes has forbidden and sometimes allowed certain degrees which the Old Law did not forbid. Therefore those degrees are an impediment to marriage.

Further, even as of old the marriages of pagans were controlled by the civil law, so now is marriage controlled by the laws of the Church. Now formerly the civil law decided which degrees of consanguinity impede marriage, and which do not. Therefore this can be done now by a commandment of the Church.

The degrees within which consanguinity has been an impediment to marriage have varied according to various times. For at the beginning of the human race father and mother alone were debarred from marrying their children, because then mankind were few in number, and then it was necessary for the propagation of the human race to be ensured with very great care, and consequently only such persons were to be debarred as were unfitted for marriage even in respect of its principal end which is the good of the offspring, as stated above (). Afterwards however, the human race having multiplied, more persons were excluded by the law of Moses, for they already began to curb concupiscence. Wherefore as Rabbi Moses says (Doc. Perp. iii, 49) all those persons were debarred from marrying one another who are wont to live together in one household, because if a lawful carnal intercourse were possible between them, this would prove a very great incentive to lust. Yet the Old Law permitted other degrees of consanguinity, in fact to a certain extent it commanded them; to wit that each man should take a wife from his kindred, in order to avoid confusion of inheritances: because at that time the Divine worship was handed down as the inheritance of the race. But afterwards more degrees were forbidden by the New Law which is the law of the spirit and of love, because the worship of God is no longer handed down and spread abroad by a carnal birth but by a spiritual grace: wherefore it was necessary that men should be yet more withdrawn from carnal things by devoting themselves to things spiritual, and that love should have a yet wider play. Hence in olden times marriage was forbidden even within the more remote degrees of consanguinity, in order that consanguinity and affinity might be the sources of a wider natural friendship; and this was reasonably extended to the seventh degree, both because beyond this it was difficult to have any recollection of the common stock, and because this was in keeping with the sevenfold grace of the Holy Ghost. Afterwards, however, towards these latter times the prohibition of the Church has been restricted to the fourth degree, because it became useless and dangerous to extend the prohibition to more remote degrees of consanguinity. Useless, because charity waxed cold in many hearts so that they had scarcely a greater bond of friendship with their more remote kindred than with strangers: and it was dangerous because through the prevalence of concupiscence and neglect men took no account of so numerous a kindred, and thus the prohibition of the more remote degrees became for many a snare leading to damnation. Moreover there is a certain fittingness in the restriction of the above prohibition to the fourth degree. First because men are wont to live until the fourth generation, so that consanguinity cannot lapse into oblivion, wherefore God threatened (Ex. 20:5) to visit the parent's sins on their children to the third and fourth generation. Secondly, because in each generation the blood, the identity of which causes consanguinity, receives a further addition of new blood, and the more another blood is added the less there is of the old. And because there are four elements, each of which is the more easily mixed with another, according as it is more rarefied it follows that at the first admixture the identity of blood disappears as regards the first element which is most subtle; at the second admixture, as regards the second element; at the third, as to the third element; at the fourth, as to the fourth element. Thus after the fourth generation it is fitting for the carnal union to be repeated.