XXVI.14 In which case, in marriages between relatives, one should go by the laws of nature, and in which case by civil laws

When it comes to the pro­hi­bi­tion of mar­riage bet­ween rela­ti­ves, it is a very deli­cate thing to find the thin line where the laws of nature stop and civil laws begin. For that, we must esta­blish some prin­ci­ples.

The mar­riage of son and mother confounds the state of things : the son owes bound­less res­pect to his mother ; the wife owes bound­less res­pect to her hus­band : the mar­riage of a mother and her son would in both cases reverse their natu­ral state.

Besides, nature has advan­ced in woman the time when she can have chil­dren, and delayed it in man ; and for the same rea­son, the woman cea­ses ear­lier to have this capa­city, and the man later. If mar­riage bet­ween mother and son were allo­wed, it would almost always result that when the hus­band was capa­ble of ente­ring into nature’s desi­gns, the woman would be no lon­ger.

Marriage bet­ween father and daugh­ter, like the pre­ce­ding one, is repu­gnant to nature ; but it is less repu­gnant, because it does not have these two obs­ta­cles. Thus the Tartars, who can marry their daugh­ters,1 never marry their mothers, as we read in the rela­tions.2

It has always been natu­ral for fathers to watch over their chil­dren’s chas­tity. Having the res­pon­si­bi­lity of esta­bli­shing them, they had to pre­serve for them both the most per­fect body and the least cor­rupt soul, all that can best incite desi­res, and all that is most apt to eli­cit affec­tion. Fathers, ever concer­ned with pre­ser­ving their chil­dren’s morals, had to have a natu­ral aver­sion to wha­te­ver could cor­rupt them. Marriage is not a cor­rup­tion, you will say ; but before the mar­riage a per­son must speak, must ins­pire loved, must entice : it is this enti­ce­ment that must have appal­led.

Therefore there had to be an insur­moun­ta­ble bar­rier bet­ween those who were to pro­vide edu­ca­tion and those who were to receive it, and they had to avoid every kind of cor­rup­tion, even for a legi­ti­mate cause. Why are fathers so intent on depri­ving those who are to marry their daugh­ters of their com­pany and fami­lia­rity ?

Horror for the incest of bro­ther with sis­ter must have come from the same source. It suf­fi­ces that fathers and mothers have wished to keep the morals of their chil­dren and their hou­ses pure, for them to have ins­pi­red hor­ror in their chil­dren for any­thing that could urge them toward the union of the two sexes.

The pro­hi­bi­tion of mar­riage bet­ween first cou­sins has the same ori­gin. In ear­liest times, in other words in holy times, in the ages when luxury was unk­nown, all chil­dren remai­ned in the house, and set­tle there, for only a very small house was requi­red for a large family.3 The chil­dren of two bro­thers, or first cou­sins, were consi­de­red, and consi­de­red them­sel­ves, as bro­thers.4 The aver­sion bet­ween bro­thers and sis­ters for mar­riage thus also exis­ted bet­ween first cou­sins.5

These cau­ses are so power­ful and so natu­ral that they have acted almost eve­ryw­here on earth, inde­pen­dently of any com­mu­ni­ca­tion. It is not the Romans who told the inha­bi­tants of Formosa6 that mar­riage with their rela­ti­ves to the fourth remove was inces­tuous ; it is not the Romans who told that to the Arabs7 ; they did not teach it in the Maldives.8

Now if some peo­ples have not rejec­ted mar­ria­ges bet­ween fathers and chil­dren, sis­ters and bro­thers, we have seen in Book I that intel­li­gent beings do not always fol­low their laws. Religious thoughts have often made men fall into these aber­ra­tions : who would have thought it ? If the Assyrians and Persians mar­ried their mothers, the for­mer did it out of reli­gious res­pect for Semiramis, and the lat­ter because the reli­gion of Zoroaster gave a pre­fe­rence to such mar­ria­ges.9 If the Egyptians mar­ried their sis­ters, that again was a folly of the Egyptian reli­gion, which conse­cra­ted those mar­ria­ges in honor of Isis. As the spi­rit of reli­gion is to impel us to do great and dif­fi­cult things with effort, we must not judge that a thing is natu­ral just because a false reli­gion has conse­cra­ted it.

The prin­ci­ple that these mar­ria­ges bet­ween fathers and chil­dren, bro­thers and sis­ters are for­bid­den for the pre­ser­va­tion of natu­ral chas­tity in the hou­se­hold will help us dis­co­ver which mar­ria­ges are for­bid­den by natu­ral law, and which can be for­bid­den only by civil law.

As the chil­dren dwell, or are assu­med to dwell, in their father’s house, and conse­quently the son-in-law with the mother-in-law, the father-in-law with the daugh­ter-in-law or with his wife’s daugh­ter, mar­riage bet­ween them is for­bid­den by the law of nature. In this case, the image has the same effect as the rea­lity, because it has the same cause : civil law nei­ther can nor should allow such mar­ria­ges.

There are peo­ples, as we have said, among whom first cou­sins are regar­ded as bro­thers because they usually dwell in the same house ; there are others where this cus­tom is quite unk­nown. In the for­mer socie­ties, mar­riage bet­ween first cou­sins should be consi­de­red contrary to nature, but not in the lat­ter.

But the laws of nature can­not be local laws. Thus, when these mar­ria­ges are for­bid­den or per­mit­ted, they are, accor­ding to the cir­cum­stan­ces, per­mit­ted or for­bid­den by a civil law.

It is not a neces­sary cus­tom for the bro­ther-in-law and sis­ter-in-law to live in the same house. Marriage is the­re­fore not for­bid­den bet­ween them to pre­serve chas­tity in the house, and the law that for­bids or per­mits it is not a law of nature, but a civil law, which varies by cir­cum­stan­ces and depends on cus­toms of each coun­try ; these are cases where the laws depend on ways or man­ners.

Civil laws for­bid mar­ria­ges when, by prac­ti­ces accep­ted in a cer­tain coun­try, they hap­pen to be in the same cir­cum­stan­ces as those which are for­bid­den by the laws of nature ; and they per­mit them when the mar­ria­ges do not fit that case. Prohibition by the laws of nature is inva­ria­ble, because it depends on some­thing inva­ria­ble : the father, the mother, and the chil­dren neces­sa­rily live in the house. But the pro­hi­bi­tions of civil laws are acci­den­tal, because they depend on an acci­den­tal cir­cum­stance : first cou­sins and others acci­den­tally living in the same house.

This explains why the laws of Moses, those of the Egyptians10 and of seve­ral other peo­ples, allow mar­riage bet­ween bro­ther-in-law and sis­ter-in-law, while those same mar­ria­ges are for­bid­den in other nations.

In the Indies, they have a quite natu­ral rea­son for allo­wing these sorts of mar­ria­ges. The uncle there is regar­ded as a father, and it is his duty to sup­port and esta­blish his nephews as if they were his own chil­dren : this springs from the cha­rac­ter of this peo­ple, which is good and full of huma­nity. This law or this prac­tice has pro­du­ced ano­ther one : if a hus­band has lost his wife, he does not fail to marry her sis­ter11 : and this is enti­rely natu­ral, for the new wife beco­mes the mother of her sis­ter’s chil­dren, and there is no wicked step­mo­ther.

This law of theirs is very ancient. Attila, says Priscus, in his embassy, stopped in a certain place to marry his daughter Esca – a thing allowed, he says, by the laws of the Scythians, p. 22.

Histoire des Tatares, part III, p. 236.

It was thus among the earliest Romans.

Indeed, among the Romans, they had the same name ; first cousins were called brothers.

This was true in Rome in the earliest times, until the people made a law to allow them : they wanted to favor an extremely popular man, one who had married his first cousin (Plutarch, in Roman Questions).

Recueil des voyages qui ont servi à l’établissement de la Compagnie des Indes, vol. V, part I, “Relation de l’état de l’île de Formose.”

Coran, chapter “On women.”

See François Pyrard.

They were regarded as more honorable. See Philo, De specialibus legibus quæ pertinent ad præcepta Decalogi, Paris, 1640, p. 778.

See law VIII in Codex, De incestis et inutilibus nuptiis.

Lettres édifiantes et curieuses, 14th volume, p. 403.