Thomas Aquinas

“ I answer that, All natural things are imbued with certain principles whereby they are enabled not only to exercise their proper actions, but also to render those actions proportionate to their end, whether such actions belong to a thing by virtue of its generic nature, or by virtue of its specific nature: thus it belongs to a magnet to be borne downwards by virtue of its generic nature, and to attract iron by virtue of its specific nature. ”

“ Accordingly we reply to the Sixth Objection that human nature was founded without any defect, and consequently it is endowed not only with those things without which the principal end of marriage is impossible of attainment, but also with those without which the secondary end of marriage could not be obtained without difficulty: and in this way it sufficed man when he was first formed to have one wife, as stated above. ”

“ Now just as in those things which act from natural necessity the principle of action is the form itself, whence their proper actions proceed proportionately to their end, so in things which are endowed with knowledge the principles of action are knowledge and appetite. ”

“ Hence it is evident that by taking several wives a man does not bind himself to the impossible, considering the principal end of marriage; and therefore plurality of wives is not against the first principles of the natural law. ”

“ The offspring, considered as one of the marriage goods, includes the keeping of faith with God, because the reason why it is reckoned a marriage good is because it is awaited with a view to its being brought up in the worship of God. Now the faith to be kept with God is of greater import than the faith to be kept with a wife, which is reckoned a marriage good, and than the signification which pertains to the sacrament, since the signification is subordinate to the knowledge of faith. ”

“ Accordingly if an action be improportionate to the end, through altogether hindering the principal end directly, it is forbidden by the first precepts of the natural law, which hold the same place in practical matters, as the general concepts of the mind in speculative matters. ”

“ Now fornication was not forbidden by positive law; indeed according to the ancient laws women used to be sentenced to be taken to brothels. Therefore it is not against the natural law to have a concubine.
Objection 3: Further, the natural law does not forbid that which is given simply, to be given for a time or under certain restrictions. Now one unmarried woman may give the power of her body for ever to an unmarried man, so that he may use her when he will. Therefore it is not against the law of nature, if she give him power of her body for a time. ”

“ Dispensation from a law should follow the quality of the law. Wherefore, since the law of nature is imprinted on the heart, it was not necessary for a dispensation from things pertaining to the natural law to be given under the form of a written law but by internal inspiration. ”

“ Further, whatever is against the natural desire is contrary to the natural law. Now a husband's jealousy of his wife and the wife's jealousy of her husband are natural, for they are found in all. Therefore, since jealousy is "love impatient of sharing the beloved," it would seem to be contrary to the natural law that several wives should share one husband. ”

“ Thus we have the aforesaid definition, namely: "Natural right is what nature has taught all animals." Accordingly plurality of wives, though not contrary to natural right taken in the third sense, is nevertheless against natural right taken in the second sense, because it is forbidden by the Divine law. It is also against natural right taken in the first sense, as appears from what has been said, for such is nature's dictate to every animal according to the mode befitting its nature. ”

“ This precept of the natural law, "Do not to another what thou wouldst not were done to thyself," should be understood with the proviso that there be equal proportion. For if a superior is unwilling to be withstood by his subject, he is not therefore bound not to withstand his subject. ”

“ Wherefore it is evident that those dictates of the natural law, which are derived from the first principles as it were of the natural law, have not the binding force of an absolute commandment, except when they have been sanctioned by Divine or human law. ”

“ Now since the rearing and teaching of the children remain a duty of the parents during a long period of time, the law of nature requires the father and mother to dwell together for a long time, in order that together they may be of assistance to their children. Hence birds that unite together in rearing their young do not sever their mutual fellowship from the time when they first come together until the young are fully fledged. ”

“ And since nature is contradistinguished with reason, whereby man is a man, it follows that if we take natural right in its strictest sense, those things which are dictated by natural reason and pertain to man alone are not said to be of natural right, but only those which are dictated by natural reason and are common to man and other animals. ”

“ Furthermore it has another end, as regards marriage between believers, namely the signification of Christ and the Church: and thus the "sacrament" is said to be a marriage good. Wherefore the first end corresponds to the marriage of man inasmuch as he is an animal: the second, inasmuch as he is a man; the third, inasmuch as he is a believer. Accordingly plurality of wives neither wholly destroys nor in any way hinders the first end of marriage, since one man is sufficient to get children of several wives, and to rear the children born of them. ”

“ In certain cases no evil results ensue if a person surrenders his right to a thing whether absolutely or for a time, so that in neither case is the surrender against the natural law. But that does not apply to the case in point, wherefore the argument does not prove. ”

“ Since, however, human acts must needs vary according to the various conditions of persons, times, and other circumstances, the aforesaid conclusions do not proceed from the first precepts of the natural law, so as to be binding in all cases, but only in the majority. ”

“ Accordingly to make use of sexual intercourse on account of its inherent pleasure, without reference to the end for which nature intended it, is to act against nature, as also is it if the intercourse be not such as may fittingly be directed to that end. ”

“ Now the begetting of offspring, though not wholly voided (since a woman may be impregnated a second time after impregnation has already taken place, as stated in De Gener. Animal. vii. 4) , is nevertheless considerably hindered, because this can scarcely happen without injury either to both fetus or to one of them. ”