By Ned Markosian, available in Dean Zimmerman (ed.), Oxford Studies in Metaphysics, Volume 1 (Oxford University Press, 2004), pp. 47-82. Reprinted in Michael Rea (ed.), Arguing About Metaphysics (Routledge, 2009); and in Sally Haslanger and Roxanne Marie Kurtz (eds.), Persistence: Contemporary Readings (MIT Press, 2006), as well as at his website.