What Did Thomas Aquinas Say About Polygamy?
Saint Thomas Aquinas (c. 1225 – March 7, 1274) was a renowned Roman Catholic priest, a theologian and philosopher. Aquinas is considered by many to be the most important Catholic theologian in history.

Thomas Aquinas noted that the biblical patriarchs David and Solomon had numerous wives. How does one explain that? Aquinas commented in his Sentences that, under certain circumstances, polygamy was reasonable and was not inconsistent with the primary purpose of marriage.

In Aquinas' Summa against the Gentiles, he developed his thought on the "three ends of marriage," later on to be taught as Catholic teaching on marriage. The test end is the bringing forth and the education of children. The second end is the common life enjoyed by the spouses. The third end is the sacramental sign given by the fidelity of one man to one woman. The last end, he said, was distinctly Christian. Of the three ends, only the third is ruled out by polygamy. The primary end is not compromised at all. So according to Aquinas, although monogamy was the optimal form of marriage, polygamy was not intrinsically evil.