We cannot tell the precise moment when friendship is formed. As in filling vessel drop by drop, there is at last a drop which makes it run over; so in a series of kindness there is at last one which makes the heart run over.

Johnson, Samuel. Quoted in The Life of Samuel Johnson, written by James Boswell, edited by David Womersley. Penguin Classics, 2008.

Paine, Thomas. "Common Sense." Rights of Man, Common Sense, and Other Political Writings, edited by Mark Philp. Oxford University Press, 2009, introduction.

Emerson, Ralph Waldo. "Friendship." The Essential Writings of Ralph Waldo Emerson, edited by Brooks Atkinson. Modern Library, 2000.

Mozart, Wolfgang Amadeus. The Letters of Mozart and His Family, edited by Emily Anderson. Springer, 2016.