TRIGENIA. - It is a particular kind of affinity (v.), at present taken into consideration only by the canon law of certain communities of the Greek rite.
In all the Eastern rites the affinity between each spouse and the relatives of the other is in force, and for Catholics it constitutes a diriment impediment to marriage up to and including the fourth degree: this is, as an amendment to what is set out in the entry AFFINITY, the law in force since 2 May 1949 (motu proprio Crebrae allatae, 22 Feb. 1949, cann. 67 § 1, no. 1, 68 § 1). In certain rites, moreover, the bond existing between the relatives of one spouse and the relatives of the other is also taken into consideration as affinity: this too, at present, constitutes a matrimonial impediment up to and including the fourth degree; and its degrees are calculated by adding together the respective degrees of kinship of each of the two affines with his relative by marriage (motu proprio cit., cann. 67 § 2, 2). Both these kinds of affinity are called affinity by digenia (ἐκ ἄγγειλς), inasmuch as two stocks are involved in it, namely that of the husband's relatives and that of the wife's relatives.
T. can occur in two cases: 1) when a person contracts several marriages in succession; 2) when two or more married persons are related to one another (motu proprio, cit., can. 68, § 3, n. 1).
In the first case t. exists between those who have contracted marriage with the same person (being, however, of the same sex, t. in this case is of little importance, even if they are all living); and moreover between each of them and the relatives of the others (motu proprio, cit., can. 68 § 3, n. 2); and, in some communities, also between the relatives of each of them and the relatives of the others (motu proprio, cit., can. 68 § 3, n. 4).
In the diagram given above there will therefore be t. between B and C, between B and e-l, and between C and a-d; moreover, in the communities in which t. is more extensive, a-d too will be affines by t. of e-l.
In the second case t. exists between each spouse and those who, by reason of another marriage, have affinity by digenia with the other spouse; and moreover, in some communities, also between the relatives of that spouse and these affines (can. 68 § 3, nn. 2 and 4).
T. will therefore exist, on the basis of these diagrams, between A and D, d, e, f, as well as between D and A, a, b; in the communities that regard t. more extensively, it will moreover exist for a, b with respect to d, e, f.
T., where it is in force, is a matrimonial impediment only in the first degree.
The computation of the degrees of t. is done, in ordinary cases, by computing as the degree of t. of each person toward one spouse the same degree in which he is an affine by digenia toward the other spouse by reason of another marriage; in cases of t. extended to the relatives of the spouse, the respective degrees of affinity by digenia and of kinship are added together, in order to obtain the degree of affinity by t. (motu proprio, cit., can. 68 § 3, nn. 3-4). No rule is laid down for computing the degree of t. between those who have contracted marriage with the same person, since this t. is not relevant as a matrimonial impediment: but it is evident that, this being the closest possible degree of t., it must be considered of the first degree.
The name affinity by t. (ἐκ τριγενείας) derives from the fact that in every case of t. three stocks or families are involved, namely those of each of the parties to the two marriages that give rise to the t.: they are three, and not four, because either one party is common to the two marriages, or a party to one is a relative of a party to the other and they therefore belong to a single stock.
Affinity by t. was known also to Latin canon law, at least in the 11th-12th centuries; and, naturally, it constituted in the West too a kind of puzzle. Therefore Innocent III, with can. 50 of the Second Lateran Council (1216), abolished in the Latin Church affinity by t., as well as the second kind of affinity by digenia.
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