The argument of this chapter is that the complexity of biological objects generates a plurality of theories, models, and explanations. With this antireductionist picture of science come new questions. In what relationship do these multiple accounts stand to one another or to the objects they describe? If there is not one, or a few, laws of biology from which all else can be explained, then how can we judge which of the infinite possible generalizations or explanations should be accepted and which not? If there is a pluralism to be had, what kind of pluralism is it?

In this chapter I first consider why reduction is attractive as an account of the relationship among scientific theories. I then argue that it fails, and pluralism is a better model. I consider two defenses of pluralism, one by John Dupré (1983, 1993, 1996), the other by Paul Sherman (1988, 1989) in the spirit of Niko Tinbergen, and reject both of these as inadequate. In the first, Dupré argues for a degree of promiscuity of taxonomies and theories that seems to me to be too unrestrained. His defense of pluralism, or disunity as he calls it, is intriguing but, I argue, ultimately fails. I propose a different argument to support a picture of pluralism that is sympathetic to, if not coextensive with, the one suggested by Dupré.