In Robert P. George (ed.), The Autonomy of Law:  Essays on Legal Positivism (Oxford University Press, 1996). Reprinted in David McLean (ed.), Common Truths:  New Perspectives on the Natural Law (ISI Books, 1999); in Aileen Kavanagh and John Oberdiek, Arguing about Law (Routledge, 2009); and in Spanish translation in Persona y Derecho 39 (1998).

Online:
Oxford University Press
Witherspoon Institute [pdf]