Whether it was ever lawful to have a concubine?

❌ Objection 1 : It would seem that it has been sometimes lawful to have a concubine. For just as the natural law requires a man to have but one wife, so does it forbid him to have a concubine. Yet at times it has been lawful to have several wives. Therefore it has also been lawful to have a concubine.

❌ Objection 2 : Further, a woman cannot be at the same time a slave and a wife; wherefore according to the Law (Dt. 21:11, seqq.) a bondswoman gained her freedom by the very fact of being taken in marriage. Now we read that certain men who were most beloved of God, for instance Abraham and Jacob, had intercourse with their bondswomen. Therefore these were not wives, and consequently it was sometime lawful to have a concubine.

❌ Objection 3 : Further, a woman who is taken in marriage cannot be cast out, and her son should have a share in the inheritance. Yet Abraham sent Agar away, and her son was not his heir (Gn. 21:14). Therefore she was not Abraham's wife.