Spheres of Reason: New Essays in the Philosophy of Normativity. : Oxford University Press, 2009-10-01. Oxford Scholarship Online. 2010-02-01. Date Accessed 18 May. 2013 <http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199572939.001.0001/acprof-9780199572939>.
(2009-10-01). Spheres of Reason: New Essays in the Philosophy of Normativity. : Oxford University Press. Retrieved 18 May. 2013, from http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199572939.001.0001/acprof-9780199572939.
Spheres of Reason: New Essays in the Philosophy of Normativity. : Oxford University Press, 2009-10-01. http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199572939.001.0001/acprof-9780199572939.
Robertson S. Spheres of Reason: New Essays in the Philosophy of Normativity. Oxford University Press; 2009. http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199572939.001.0001/acprof-9780199572939. Accessed May 18, 2013.