"Credo". Essay by Arthur C. Clarke (1991), later published in Arthur C. Clarke "Greetings, Carbon-Based Bipeds!: Collected Essays, 1934-1998" (p. 360), 1999.
Charles Darwin (2010). “The Works of Charles Darwin, Volume 29: “Erasmus Darwin” by Ernest Krause, with a Preliminary Notice by Charles Darwin; “The Autobiography of Charles Darwin” Edited by Nora Barlow; and Consolidated Index”, p.124, NYU Press
Rene Descartes (2013). “Discourse on the Method: Discourse On the Method of Rightly Conducting the Reason, and Seeking Truth In the Sciences (Beloved Books Edition)”, p.30, Lulu Press, Inc