Falcon, Andrea: Commentators on AristotleThe Stanford Encyclopedia of Philosophy. The Metaphysics Research Lab. Stanford University. Viitattu 5.10.2012. (englanniksi)
Gracia, Jorge & Newton, Lloyd: Medieval Theories of the CategoriesThe Stanford Encyclopedia of Philosophy. The Metaphysics Research Lab. Stanford University. Viitattu 5.10.2012. (englanniksi)