על החוקים לפרטיהם, ספר ג ד׳On the Special Laws, Book III 4
א׳
1[22] Next comes a prohibition against espousing a sister, a very excellent rule tending to promote both continence and outward decency. Now Solon the lawgiver of the Athenians permitted marriage with half-sisters on the father’s side but prohibited it when the mother was the same. The lawgiver of the Lacedaemonians, on the other hand, allowed the second but forbade the first.
ב׳
2[23] But the lawgiver of the Egyptians poured scorn upon the cautiousness of both, and, holding that the course which they enjoined stopped half-way, produced a fine crop of lewdness. With a lavish hand he bestowed on bodies and souls the poisonous bane of incontinence and gave full liberty to marry sisters of every degree whether they belonged to one of their brother’s parents or to both, and not only if they were younger than their brothers but also if they were older or of the same age. For twins are often born who, although separated and disunited by nature at birth, enter at the call of concupiscence and voluptuousness into a partnership and wedlock which are neither in the true sense of the words.
ג׳
3[24] These practices our most holy Moses rejected with abhorrence as alien and hostile to a commonwealth free from reproach and as encouragements and incitements to the vilest of customs. He stoutly forbade the union of a brother with a sister whether both her parents were the same as his or only one.
ד׳
4[25] For modesty is lovely, why put it to shame? Maidens must blush, why drive the hue from their cheeks? Why hamper the fellow-feeling and inter-communion of men with men by compressing within the narrow space of each separate house the great and goodly plant which might extend and spread itself over continents and islands and the whole inhabited world? For intermarriages with outsiders create new kinships not a wit inferior to blood-relationships.