Street, Sharon. "Constructivism About Reasons", in Shafer-Landau, Russ (ed). Oxford Studies in Metaethics, Vol. 3 (Oxford: Clarendon, 2008), pp. 207-245.*
[*] For those interested: The paper should be read along with her important paper, "A Darwinian Dilemma for Realist Theories of Value", Phil. Studies 127:1 (Jan. 2006), pp. 109-166. Of course, there has been much discussion of Steet's "Dilemma" paper since it first appeared. For an important recent defense of Street's dilemma, see Fraser, Benjamin James. "Evolutionary Debunking Arguments and the Reliability of Moral Cognition", Phil. Studies (forthcoming). The penultimate draft can be found here.