Sexual intercommunity (commercium sexuale) is the use of the other's sexual members and faculties. This use is either natural, by which human beings may reproduce their own kind, or unnatural, which, again, refers either to a person of the same sex or to an animal of another species than man. These transgressions of all law, as crimina carnis contra naturam [crimes of the flesh against nature], are even "not to be named"; and, as wrongs against all humanity in the person, they cannot be saved, by any limitation or exception whatever, from entire reprobation.
This natural union of the sexes proceeds according to the mere animal nature (vaga libido [unsettled lust], venus vulgivaga [roving sexuality], fornicatio [fornication]), or according to the law. The latter is marriage (matrimonium), which is the union of two persons of different sex for life-long reciprocal possession of their sexual faculties. The end of producing and educating children may be regarded as always the end of nature in implanting mutual desire and inclination in the sexes; but it is not necessary for the rightfulness of marriage that those who marry should set this before themselves as the end of their union, otherwise the marriage would be dissolved of itself when the production of children ceased.
And even assuming that enjoyment in the reciprocal use of the sexual endowments is an end of marriage, yet the contract of marriage is not on that account a matter of arbitrary will, but is a contract necessary in its nature by the law of humanity. In other words, if a man and a woman have the will to enter on reciprocal enjoyment in accordance with their sexual nature, they must necessarily marry each other; and this necessity is in accordance with the juridical laws of pure reason.
For, this natural employment--as a use of the sexual members of the other--is an enjoyment for which the one person is given up to the other. In this relation the human individual makes himself into a thing, which is contrary to the right of humanity in his own person. This, however, is only possible under the one condition, that as the one person is acquired by the other as a thing, that same person also equally acquires the other reciprocally, and thus regains and reestablishes the rational personality. The acquisition of a part of the human organism being, on account of its unity, at the same time the acquisition of the whole person, it follows that the surrender and acceptation of, or by, one sex in relation to the other, is not only permissible under the condition of marriage, but is further only really possible under that condition. But the personal right thus acquired is, at the same time, real in kind; and this characteristic of it is established by the fact that if one of the married persons run away or enter into the possession of another, the other is entitled, at any time, and incontestably, to bring such a one back to the former relation, as if that person were a thing.
For the same reasons, the relation of the married persons to each other is a relation of equality as regards the mutual possession of their persons, as well as of their goods. Consequently marriage is only truly realized in monogamy; for in the relation of polygamy the person who is given away on the one side, gains only a part of the one to whom that person is given up, and therefore becomes a mere thing. But in respect of their goods, they have severally the right to renounce the use of any part of them, although only by a special contract.
From the principle thus stated, it also follows that concubinage is as little capable of being brought under a contract of right as the hiring of a person on any one occasion, in the way of a pactum fornicationis [contract for fornication]. For, as regards such a contract as this latter relation would imply, it must be admitted by all that any one who might enter into it could not be legally held to the fulfillment of their promise if they wished to resile from it. And as regards the former, a contract of concubinage would also fall as a pactum turpe [shameful contract]; because as a contract of the hire (locatio, conductio), of a part for the use of another, on account of the inseparable unity of the members of a person, any one entering into such a contract would be actually surrendering as a thing to the arbitrary will of another. Hence any party may annul a contract like this if entered into with any other, at any time and at pleasure; and that other would have no ground, in the circumstances, to complain of a lesion of his right. The same holds likewise of a morganatic or "left-hand" marriage, contracted in order to turn the inequality in the social status of the two parties to advantage in the way of establishing the social supremacy of the one over the other; for, in fact, such a relation is not really different from concubinage, according to the principles of natural right, and therefore does not constitute a real marriage. Hence the question may be raised as to whether it is not contrary to the equality of married persons when the law says in any way of the husband in relation to the wife, "he shall be thy master," so that he is represented as the one who commands, and she is the one who obeys. This, however, cannot be regarded as contrary to the natural equality of a human pair, if such legal supremacy is based only upon the natural superiority of the faculties of the husband compared with the wife, in the effectuation of the common interest of the household, and if the right to command is based merely upon this fact. For this right may thus be deduced from the very duty of unity and equality in relation to the end involved.
The contract of marriage is completed only by conjugal cohabitation. A contract of two persons of different sex, with the secret understanding either to abstain from conjugal cohabitation or with the consciousness on either side of incapacity for it, is a simulated contract; it does not constitute a marriage, and it may be dissolved by either of the parties at will. But if the incapacity only arises after marriage, the right of the contract is not annulled or diminished by a contingency that cannot be legally blamed. The acquisition of a spouse, either as a husband or as a wife, is therefore not constituted facto [by the deed]--that is, by cohabitation--without a preceding contract; nor even pacto [by the contract]--by a mere contract of marriage, without subsequent cohabitation; but only lege [by law], that is, as a juridical consequence of the obligation that is formed by two persons entering into a sexual union solely on the basis of a reciprocal possession of each other, which possession at the same time is only effected in reality by the reciprocal use of the other's sexual faculties.