Leviticus 18:9

“The nakedness of thy sister, etc.] To lie with one in so near a relation is exceeding criminal, and for which the law curses a man, (<052722>Deuteronomy 27:22); and to marry her is not lawful; for though it was necessary for the propagation of mankind that a man should marry his sister, for who else could Cain and Abel marry? yet afterwards, when there was an increase of mankind, and there were people enough remote from each other, it became unlawful for persons in such near ties of consanguinity to marry with each other; though the Egyptians did, in imitation of Isis and Osiris f627, and so the Persians, following the example of Cambyses f628: the daughter of thy father, or the daughter of…”

“Thy sister - What was here spoken of was the distinguishing offence of the Egyptians. return to 'Top of Page'”

“18:9 Sexual relations with a full sister dishonored both parents, and relations with a half sister dishonored one parent.”

“Lev 20:17; Deu 27:22; Sa2 13:11-14; Eze 22:11 Leviticus 18:12”

“By the sister, the daughter of father or mother, we are to understand only the step-or half-sister, who had either the same father or the same mother as the brother had. The clause, "whether born at home or born abroad," does not refer to legitimate or illegitimate birth, but is to be taken as a more precise definition of the words, daughter of thy father or of thy mother, and understood, as Lud. de Dieu supposes, as referring to the half-sister "of the first marriage, whether the father's daughter left by a deceased wife, or the mother's daughter left by a deceased husband," so that the person marrying her would be a son by a second marriage. Sexual intercourse with a half-sister is…”