Kurt Vonnegut (2016). “If This Isn't Nice What Is? (Much) Expanded Second Edition: The Graduation Speeches and Other Words to Live By”, p.131, RosettaBooks
Ralph Waldo Emerson, Alfred R. Ferguson (1965). “Journals and Miscellaneous Notebooks of Ralph Waldo Emerson, Volume V: 1835-1838”, p.233, Harvard University Press