The Four-Category Ontology: A Metaphysical Foundation for Natural Science. : Oxford University Press, 2005-12-01. Oxford Scholarship Online. 2006-05-01. Date Accessed 22 May. 2013 <http://www.oxfordscholarship.com/view/10.1093/0199254397.001.0001/acprof-9780199254392>.
(2005-12-01). The Four-Category Ontology: A Metaphysical Foundation for Natural Science. : Oxford University Press. Retrieved 22 May. 2013, from http://www.oxfordscholarship.com/view/10.1093/0199254397.001.0001/acprof-9780199254392.
The Four-Category Ontology: A Metaphysical Foundation for Natural Science. : Oxford University Press, 2005-12-01. http://www.oxfordscholarship.com/view/10.1093/0199254397.001.0001/acprof-9780199254392.
Lowe EJ. The Four-Category Ontology: A Metaphysical Foundation for Natural Science. Oxford University Press; 2005. http://www.oxfordscholarship.com/view/10.1093/0199254397.001.0001/acprof-9780199254392. Accessed May 22, 2013.