Immanuel Kant (2015). “The Critique of Practical Reason: Theory of Moral Reasoning: From the Author of Critique of Pure Reason, Critique of Judgment, Dreams of a Spirit-Seer, Perpetual Peace & Fundamental Principles of the Metaphysics of Morals”, p.51, e-artnow
Epistola ad Posteros [Letter to Posterity] in "Petrarch : The First Modern Scholar and Man of Letters" by James Harvey Robinson and Henry Winchester Rolfe, (p. 59), 1898.