One man to one woman is the law of God and nature.
 Plato, The Republic. copy citation

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Author Plato
Source The Republic
Topic God women
Date
Language English
Reference
Note Translated by Benjamin Jowett
Weblink http://www.gutenberg.org/files/1497/1497-h/1497-h.htm

Context

“, and also because any departure from established morality, even where this is not intended, is apt to be unsettling, it may be worth while to draw out a little more at length the objections to the Platonic marriage. In the first place, history shows that wherever polygamy has been largely allowed the race has deteriorated. One man to one woman is the law of God and nature. Nearly all the civilized peoples of the world at some period before the age of written records, have become monogamists; and the step when once taken has never been retraced. The exceptions occurring among Brahmins or Mahometans or the ancient Persians, are of that sort which may be said to prove the rule.” source