“Between two married couples there are five possibilities for friendship: man to man, woman to woman, each man to the woman not his wife, and couple to couple. It's seldom that more than two of these will actually materialize.”
The Complete Neurotic's Notebook (1981), Marriage
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Mignon McLaughlin 278
American journalist 1913–1983Related quotes

The allegation that Catharine MacKinnon equated sex with rape, or suggested that all sex is hostile, seems to have been first made in the October 1986 issue of Playboy. Catharine MacKinnon has denied ever saying anything of the kind. http://www.snopes.com/quotes/mackinno.htm
Instead MacKinnon asserts that rape and intercourse are "difficult to distinguish" (1983), and that "the major distinction between intercourse (normal) and rape (abnormal) is that the normal happens so often that one cannot get anyone to see anything wrong with it" (1989).
Misattributed

“Man and woman are two locked caskets, of which each contains the key to the other.”
"A Consolatory Tale"
Winter's Tales (1942)

Interview in Speaking Frankly by Wendy Leigh (London: Muller, 1978).
The Complete Neurotic's Notebook (1981), Women & men

“A man can sometimes hold his own with one woman, but never with two.”
Source: John Jerome: His Thoughts and Ways (1886), Ch. 12, p. 207.

"A Painful Case"
Source: Dubliners (1914)
Context: One of his sentences, written two months after his last interview with Mrs. Sinico, read: Love between man and man is impossible because there must not be sexual intercourse and friendship between man and woman is impossible because there must be sexual intercourse.

“Behind every successful man is a woman, behind her is his wife.”