Sexual intercourse (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, 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, venus vulgivaga, fornicatio), 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.
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.
The contract of marriage is completed only by conjugal cohabitation.
Immanuel Kant, "The science of right" + Vogue Paris Fevrier 08, x la genial Emmanuelle Alt
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