This paper argues against the realization principle, which reifies the realization relation between lower-level and higher-level properties. It begins with a review of some principles of naturalistic metaphysics. Then it criticizes some likely reasons for embracing the realization principle, and finally it argues against the principle directly. The most likely reasons for embracing the principle depend on the dubious assumption that special science theories cannot be true unless special science predicates designate properties. The principle itself turns out to be false (...) because the realization relation fails the naturalistic test for reality: it makes no causal difference to the world.Footnote11This paper resulted from work done at John Heil's 2006 Mind and Metaphysics NEH Summer Seminar at Washington University in St. Louis. An early version of it was presented in a special symposium on realization at the 2007 meeting of the Southern Society for Philosophy and Psychology. I owe thanks to all the participants in both events for helpful discussions, and I owe particular thanks to Ken Aizawa, Torin Alter, Jason Ford, Carl Gillett, John Heil, Nicholas Helms, Pete Mandik, John Post, Gene Witmer, Michelle Wrenn, Tad Zawidzki, and two anonymous referees for the AJP. (shrink)