If a man does not make new acquaintance as he advances through life, he will soon find himself left alone. A man, Sir, should keep his friendship in constant repair.

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

Madison, James. "No. 47: Complete separation of powers not required.--Madison." The Federalist: A Commentary on the Constitution of the United States, edited by Robert Scigliano. The Modern Library, 2001.

Aristotle. Quoted in The Lives of Eminent Philosophers, written by Diogenes Laërtius, translated by Pamela Mensch, edited by James Miller. Oxford University Press, 2018, bk. 5, ch. 1, sect. 20.