↑ Seymour-Smith, Maerin (1998). The 100 Most Influential Books Ever Written: The History of Thought from Ancient Times to Today. Secaucus, NJ: Citadel Press.
↑ The Great Philosophers, by Jeremy Stangroom and James Garvey, Arcturus 2005/ 2008 ISBN 978-1-84837-018-0, pp160 UKP9.99
