Of all the means which wisdom acquires to ensure happiness throughout the whole of life, by far the most important is friendship.

Socrates. Quoted in The Lives of Eminent Philosophers, written by Diogenes Laërtius, translated by Pamela Mensch, edited by James Miller. Oxford University Press, 2018, bk. 2, ch. 5.

Aristotle. Nicomachean Ethics, translated by Terence Irwin. Hackett Publishing, 2019, bk. 8.

Tibullus. Elegies: With Paralell Latin Texts, translated by A. M. Juster. Oxford University Press, 2012, bk. 1, no. 1.

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. 17.