“Friendship: A ship big enough for two in fair weather, but only one in foul.”

Act i. Sc. 3.
The Marriage of Guenevere (1891)

as quoted in "Keynes and the Ethics of Capitalism" by Robert Skidelsy http://www.webcitation.org/query?id=1256603608595872&url=www.geocities.com/monedem/keyn.html
Essays in Persuasion (1931), Economic Possibilities for our Grandchildren (1930)
Context: When the accumulation of wealth is no longer of high social importance, there will be great changes in the code of morals. We shall be able to rid ourselves of many of the pseudo-moral principles which have hag-ridden us for two hundred years, by which we have exalted some of the most distasteful of human qualities into the position of the highest virtues. We shall be able to afford to dare to assess the money-motive at its true value. The love of money as a possession — as distinguished from the love of money as a means to the enjoyments and realities of life — will be recognised for what it is, a somewhat disgusting morbidity, one of those semi-criminal, semi-pathological propensities which one hands over with a shudder to the specialists in mental disease … But beware! The time for all this is not yet. For at least another hundred years we must pretend to ourselves and to everyone that fair is foul and foul is fair; for foul is useful and fair is not. Avarice and usury and precaution must be our gods for a little longer still. For only they can lead us out of the tunnel of economic necessity into daylight.

Crazy Jane Talks With The Bishop http://poetry.poetryx.com/poems/1471/, st. 2
The Winding Stair and Other Poems (1933)

Act IV, sc. i
Le Bourgeois Gentilhomme (1670)

Source: Macbeth

Source: A Corner of the Universe, ~pg 107; Adam on friendship

Source: Argonautica (3rd century BC), Book IV. Homeward Bound, Lines 933–938 (tr. R. C. Seaton)