There is a present effort being made by many anti-homosexual moralists to statutize the legal definition of 'marriage' to be a social union between "one man and one woman." Notice the cutesy catch-phrase sloganizing. Sort of has a rhyme and rhythm to it.
In advocating such, those moralists are not only prohibiting same-sex/same-gender 'marriages' [actually the sickening non-CIVIL-union of the pervert dogs of sodomy] plus prohibiting whatever-gender group-combo 'marriages,' but also illegalizing multiple-wife polygamy.....which would make what many of the Old Testament patriarchs did (and what some of the modern-day arab sheiks do with their multiple-wife harems) constitute unlawful bigamy.
In view of that, this webauthor of course prefers statutizing 'marriage' as "a social union of a man and woman" - which obviously leaves open the possibility of having simultaneous multi-woman sexual relations (whether the women involved are 'wives' or 'concubines').
Now, before any of you who are moralists see red, may I remind you first that God never specifically condemned any Old-Testament patriarchs (and there were many, such as Lamech (Gen. 4:19,23), Esau (Gen. 28:9, 36:2), Jacob (Gen. 29), Gideon (Judges 8:30), Elkanah (I Sam. 1:2), David (I Sam 25:43, 27:3, 30:5, II Sam. 5:13), Solomon (I Kings 11:3), Ashhur (I Chron. 4:5), Rehoboam (II Chron. 11:21), Abijah (II Chron. 13:21), Jehoiadah (II Chron. 24:3)....who had multiple wives and concubines. Wise old Solomon (in Ecclesiastes 2:8) informs us that it is man's delight to have many concubines (if one can afford them, though Solomon was not wise in his choice of foreign wives who turned his heart to idol worship). In fact, God Himself giving the Mosaic law within the Holy Pentateuch specifically cites what to do in the case of a man having two wives (Deuteronomy 21:15). Not forbidding ALL men from having multiple wives and concubines, Saint Paul merely disallowed bishops and deacons from being polygamous (I Timothy 3:2,12 and Titus 1:6).
Also keep in mind that those additional women were NOT harlots, whores, sluts, prostitutes, nor anything of the like....in that they always and only belonged to the one man who was the male of the harem.
One would perhaps wonder why a man would get an additional common-law wife or concubine besides the one he legally owned in our 21st-century society (and a mistress of adultery is out of the question). Is the present singular wife too old and thus getting too ugly compared to how she once looked and erotically performed? Is she getting anti-sensually and frigidly sexist, prudish, and noncooperative sexually? Has God called a younger women to take the initiative to make known to an already-married man her sacred intention of supplementing what the man's primary wife simply cannot do or does not want done erotically?
Be reminded that we are not talking about a fornication nor adultery-minded masseuse or escort here. We are instead referring to a saintly young lady who is quite modestly dressed in public and discreetly faithful to the shared man she also considers her husband, respecting both his legal reputation, the priority status of his primary wife, his limited finances, and the complexity of becoming pregnant by him with the complications of consequential children being born and raised within a demonic community which is of a godlessly-restrictive 'one-man-for-ONE-woman' immentality. There are situations in which the additional concubine in a husband's life might have to accomodate to her husband's primary wife (with nun-like self-control and partial abstinence).....but to have a husband part-time is better for some than not having any husband at all or resorting to the self-sodomizing masturbation condemned in First Corinthians 6:9-10.
If women who share the same husband discover each other, the very real potential for rival jealousy exists, as in fact happened in the case of Rachel, Leah, and their maids they gave to Jacob to procreate with. Such also was true in the case of Elkanah's two wives, where the one persecuted the other. However, one should not presume that a husband with multiple wives hates one and exclusively loves the other, but simply that he prefers one over the other at times because of situational opportunity relating to his biological needs, the aggressiveness towards him of whichever of his wives or concubines, and the temporary circumstantial unavailability or incapacity of whichever of his wives or concubines.