Thomas Aquinas

“ But the marriage of relatives by affinity and consanguinity is unlawful. Therefore it can be denounced.
I answer that, Accusation is instituted lest the guilty be tolerated as though they were innocent. Now just as it happens through ignorance of fact that a guilty man is reputed innocent, so it happens through ignorance of a circumstance that a certain fact is deemed lawful whereas it is unlawful. Wherefore just as a man is sometimes accused, so is a fact sometimes an object of accusation. ”

“ I answer that, Just as a betrothal has not the conditions of a perfect marriage, but is a preparation for marriage, so betrothal causes not affinity as marriage does, but something like affinity. This is called "the justice of public honesty," which is an impediment to marriage even as affinity and consanguinity are, and according to the same degrees, and is defined thus: "The justice of public honesty is a relationship arising out of betrothal, and derives its force from ecclesiastical institution by reason of its honesty." ”

“ Although the Church is upheld by God's gift and authority, yet in so far as she is an assembly of men there results in her acts something of human frailty which is not Divine. Therefore a union effected in the presence of the Church who is ignorant of an impediment is not indissoluble by Divine authority, but is brought about contrary to Divine authority through man's error, which being an error of fact excuses from sin, as long as it remains. Hence when the impediment comes to the knowledge of the Church, she ought to sever the aforesaid union. ”

“ If the marriage is not yet contracted and there is only a betrothal, there can be no accusation, for what is not, cannot be accused. But the impediment can be denounced lest the marriage be contracted. ”

“ The punishment of retaliation takes place when a person is accused of a crime, because then action is taken that he may be punished. But when it is a deed that is accused, action is taken not for the punishment of the doer, but in order to prevent what is unlawful. Hence in a matrimonial suit the accuser does not bind himself to a punishment. Moreover, the accusation may be made either in words or in writing, provided the person who denounces the marriage denounced, and the impediment for which it is denounced, be expressed. ”

“ Further, consanguinity is a stronger tie than affinity. But the blood-relations of the wife do not become blood-relations of the husband. Much less, therefore, does affinity to the wife cause affinity to her blood-relations, and thus the same conclusion follows.
I answer that, There are two ways in which one thing proceeds from another: in one way a thing proceeds from another in likeness of species, as a man is begotten of a man: in another way one thing proceeds from another, not in likeness of species ”

“ All those impediments which void a betrothal prevent affinity being contracted through a promise of marriage. Hence whether he who actually promises marriage be lacking in age, or be under a solemn vow of continence or any like impediment, no affinity nor anything akin to it results because the betrothal is void. ”

“ Although a cause is more potent than its effect, it does not always follow that the same name is applicable to the cause as to the effect, because sometimes that which is in the effect, is found in the cause not in the same but in a higher way ”

“ Hence he is not bound to form his conscience on what has been done about the other marriage: but seemingly one ought to draw a distinction, because either he has certain knowledge of the impediment of his marriage, or he has an opinion about it, or he has neither. ”

“ Now aptitude for movement and for being moved is transitory; whereas the fact of having been moved is everlasting, since what has been never ceases having been. Consequently fatherhood and sonship are never dissolved through the removal of the cause, but only through the corruption of the subject, that is of one of the subjects. The same applies to affinity, for this is caused by certain persons having been joined together not by their being actually joined. ”

“ In an unlawful intercourse there is something natural which is common to fornication and marriage, and in this respect it causes affinity. There is also something which is inordinate whereby it differs from marriage, and in this respect it does not cause affinity. ”

“ Further, a relation results sometimes from a movement in each extreme, for instance fatherhood and sonship, and a relation of this kind is really in both extremes. Sometimes it results from the movement of one only, and this happens in two ways. In one way when a relation results from the movement of one extreme without any movement previous or concomitant of the other extreme; as in the Creator and the creature, the sensible and the sense, knowledge and the knowable object: and then the relation is in one extreme really and in the other logically only. ”

“ Wherefore a stranger is debarred from accusing when there are relatives who are silent, and by whom he cannot prove his accusation. On the other hand the relatives, however nearly related they be, are not debarred from accusing, when the marriage is denounced on account of a perpetual impediment, which prevents the contracting of the marriage and voids the contract. ”

“ A husband contracts affinity of the first kind with his wife's male blood-relation, and affinity of the second kind with the latter's wife: wherefore if the latter man dies the former cannot marry his widow on account of the second kind of affinity. Again if a man A marry a widow B, C, a relation of her former husband being connected with B by the first kind of affinity, contracts affinity of the second kind with her husband A ”

“ Consequently even as a person through being connected with another by carnal procreation is bound to him by a tie of natural friendship, so does one person become connected with another through carnal intercourse. ”

“ Further, if certain things be separate from one another and something be connected with one of them, it does not follow that it is connected with the other. Now a person's blood relations are separate from one another. Therefore it does not follow, if a certain woman be married to a certain man, that she is therefore connected with all his kindred. ”

“ Strangers cannot know of the consanguinity except from the relatives, since these know with greater probability. Hence when these are silent, a stranger is liable to be suspected of acting from ill-will unless he wish the relatives to prove his assertion. ”

“ Further, betrothal is nothing but a promise of future marriage. Now sometimes there is a promise of future marriage without affinity being contracted, for instance if it take place before the age of seven years; or if a man having a perpetual impediment of impotence promise a woman future marriage ”

“ The first kind of procession, however often it be repeated, the same species always remains: thus if one man be begotten of another by an act of the generative power, of this man also another man will be begotten, and so on. ”

“ I answer that, In this kind of lawsuit as in others, truth must be unveiled by witnesses: yet, as the lawyers say, there are many things peculiar to this suit; namely that "the same person can be accuser and witness; that evidence is not taken 'on oath of calumny,' since it is a quasi-spiritual lawsuit; that relatives are allowed as witnesses; that the juridical order is not perfectly observed, since if the denunciation has been made, and the suit is uncontested, the defendant may be excommunicated if contumacious; that hearsay evidence is admitted ”

“ In contentious suits between two persons the verdict does not prejudice a third party, wherefore although the one brother's marriage with the one sister is annulled on account of consanguinity, the Church does not therefore annul the other marriage against which no action is taken. ”

“ When, however, the accusation is based on a denial of the contract having taken place, the parents should be debarred from witnessing as being liable to suspicion, except those of the party that is inferior in rank and wealth, for they, one is inclined to think, would be willing for the marriage to stand. ”

“ Further, witnesses who are suspected of private hatred or love are debarred from giving evidence. Now relatives are especially open to suspicion of love for one party, and hatred for the other. Therefore their evidence should not be taken. ”

“ But the second kind of procession, just as in the first instance it produces another species, so it makes another species as often as it is repeated. Thus by movement from a point there proceeds a line and not a point, because a point by being moved makes a line ”