Charles, David. "Definition and Demonstration: The Difficulties Raised in Posterior Analytics Β.3–7." Aristotle on Meaning and Essence. : Oxford University Press, 2002-10-10. Oxford Scholarship Online. 2003-11-01. Date Accessed 24 May. 2013 <http://www.oxfordscholarship.com/view/10.1093/019925673X.001.0001/acprof-9780199256730-chapter-8>.
Charles, D.(2002-10-10). Definition and Demonstration: The Difficulties Raised in Posterior Analytics Β.3–7. In Aristotle on Meaning and Essence. : Oxford University Press. Retrieved 24 May. 2013, from http://www.oxfordscholarship.com/view/10.1093/019925673X.001.0001/acprof-9780199256730-chapter-8.
Charles, David. "Definition and Demonstration: The Difficulties Raised in Posterior Analytics Β.3–7." In Aristotle on Meaning and Essence. : Oxford University Press, 2002-10-10. http://www.oxfordscholarship.com/view/10.1093/019925673X.001.0001/acprof-9780199256730-chapter-8.
Charles D. Definition and Demonstration: The Difficulties Raised in Posterior Analytics Β.3–7. In: Charles D. Aristotle on Meaning and Essence. Oxford University Press; 2002. http://www.oxfordscholarship.com/view/10.1093/019925673X.001.0001/acprof-9780199256730-chapter-8. Accessed May 24, 2013.