Why may a Jewish man not have two wives if the Torah doesn't explicitly forbid it?ask your rav
Before Rabbeinu Gershom's decree, the Torah did in fact permit a man to have more than one wife, though monogamy was always the normal and recommended practice; the ban isn't an objection to the Torah, but a cherem that became urgently necessary for its generation and was accepted in our lands as a binding custom. It's explained by concern for a livelihood during the poverty of exile, for women (so a husband wouldn't pressure a first wife into a get or mistreat her), for danger among nations where bigamy is a crime, for mourning the Beis HaMikdash, and for peace in the home.
Before Rabbeinu Gershom's decree, a man was permitted to have more than one wife -- a woman having more than one husband was strictly forbidden. But the normal and recommended practice in Judaism was always monogamy.
“Monogamy was always the normal and recommended practice in Judaism.”
He brings the halacha as it's recorded: Rav Yosef Karo cites Rabbeinu Gershom's cherem against marrying a second wife while the first is alive, and notes that not all countries accepted this decree, and that it was meant to hold until the end of the fifth millennium, while the Rema adds that in our lands this decree and custom remain in force, and we do not marry two wives. He then gathers the reasons later authorities give: we are in exile and poor, income is unreliable, and Rabbeinu Gershom didn't want men taking many wives and having more children than they could support; having forbidden divorce without the wife's consent, he was concerned a husband might get around it by taking a second wife and making the first one's life miserable until she agreed to a get; living among nations where bigamy is a crime, it would bring hatred and danger on us; in mourning for the Beis HaMikdash, the Gemara would in principle call for forbidding marriage altogether, but the people couldn't bear that, so it was said: one should marry, just not take more than one wife. And finally, having several wives leads to strife in the home -- the decree benefits both women and men, and it protects women from harsh husbands.
“Several wives lead to strife and discord in the home.”
He explains: Rabbeinu Gershom saw that introducing this ban had become urgently necessary for his generation. In other words, this isn't an objection to the Torah, but a decree that was needed precisely then and precisely there.
“Rabbeinu Gershom saw that this ban needed to be introduced.”
