George Santayana, Marianne S. Wokeck, Martin A. Coleman, James Gouinlock (2015). “The Life of Reason Or The Phases of Human Progress: Reason in Art, Volume VII, Book Four”, p.70, MIT Press
Mary Wollstonecraft, Janet Todd (2008). “A Vindication of the Rights of Men; A Vindication of the Rights of Woman; An Historical and Moral View of the French Revolution”, p.113, Oxford University Press
George Santayana (1937). “The Works of George Santayana: Dialogues in limbo. Platonism and the spiritual life. A long way round to Nirvana. The prestige of the infinite. Ultimate religion”