David Hume (1788). “An inquiry concerning human understanding. A dissertation on the passions. An inquiry concerning the principles of morals. The natural history of religion”, p.162
Anton Chekhov (2015). “The Life and Genius of Anton Chekhov: Letters, Diary, Reminiscences and Biography: Assorted Collection of Autobiographical Writings of the Renowned Russian Author and Playwright of Uncle Vanya, The Cherry Orchard, The Three Sisters and The Seagull”, p.321, e-artnow