That Christian marriage (i.e. marriage between baptized persons) is really a sacrament of the New Law in the strict sense of the word is for all Catholics an indubitable truth. According to the Council of Trent this dogma has always been taught by the Church, and is thus defined in canon i, Sess. XXIV: "If any one shall say that matrimony is not truly and properly one of the Seven Sacraments of the Evangelical Law, instituted by Christ our Lord, but was invented in the Church by men, and does not confer grace, let him be anathema." The occasion of this solemn declaration was the denial by the so-called Reformers of the sacramental character of marriage. Calvin in his "Institutions", IV, xix, 34, says: "Lastly, there is matrimony, which all admit was instituted by God, though no one before the time of Gregory regarded it as a sacrament. What man in his sober senses could so regard it? God's ordinance is good and holy; so also are agriculture, architecture, shoemaking, hair-cutting legitimate ordinances of God, but they are not sacraments". And Luther speaks in terms equally vigorous. In his German work, published at Wittenberg in 1530 under the title "Von den Ehesachen", he writes (p. 1): "No one indeed can deny that marriage is an external worldly thing, like clothes and food, house and home, subject to worldly authority, as shown by so many imperial laws governing it." In an earlier work (the original edition of "De captivitate Babylonica") he writes: "Not only is the sacramental character of matrimony without foundation in Scripture; but the very traditions, which claim such sacredness for it, are a mere jest"; and two pages further on: "Marriage may therefore be a figure of Christ and the Church; it is, however, no Divinely instituted sacrament, but the invention of men in the Church, arising from ignorance of the subject." The Fathers of the Council of Trent evidently had the latter passage in mind.
CATHOLIC ENCYCLOPEDIA: Sacrament of Marriage
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The word marriage may be taken to denote the action, contract, formality, or ceremony by which the conjugal union is formed or the union itself as an enduring condition. In this article we deal for the most part with marriage as a condition, and with its moral and social aspects. It is usually defined as the legitimate union between husband and wife. "Legitimate" indicates the sanction of some kind of law, natural, evangelical, or civil, while the phrase, "husband and wife", implies mutual rights of sexual intercourse, life in common, and an enduring union. The last two characters distinguish marriage, respectively, from concubinage and fornication. The definition, however, is broad enough to comprehend polygamous and polyandrous unions when they are permitted by the civil law; for in such relationships there are as many marriages as there are individuals of the numerically larger sex. Whether promiscuity, the condition in which all the men of a group maintain relations and live indiscriminately with all the women, can be properly called marriage, may well be doubted. In such a relation cohabitation and domestic life are devoid of that exclusiveness which is commonly associated with the idea of conjugal union.
CATHOLIC ENCYCLOPEDIA: History of Marriage