Henry David Thoreau, Jeffrey S. Cramer (2007). “I to Myself: An Annotated Selection from the Journal of Henry D. Thoreau”, p.170, Yale University Press
Socrates, Plato, Aristotle (1967). “Wit and Wisdom of Socrates, Plato, Aristotle: Being a Treasury of Thousands of Glorious, Inspiring and Imperishable Thoughts, Views and Observations of the Three Great Greek Philosophers, Classified Under about Four Hundred Subjects for Comparative Study”
H. Jackson Brown, Jr. (2012). “Life's Little Instruction Book: Simple Wisdom and a Little Humor for Living a Happy and Rewarding Life”, p.498, Thomas Nelson Inc