For most Americans the terms “environmentalist” and “liberal” are more or less synonymous. For many historians the set of ideas called environmentalism and the set of ideas called liberalism are similarly—and for similar reasons—connected. But it is not at all clear why these associations make sense. The environmental historian Roderick Nash provides one explanation for the pairing of environmentalism and liberalism in The Rights of Nature, where he argues that “one can regard environmental ethics as marking out the farthest limits of American liberalism.” 1 For Nash, the association is a direct one: environmentalism and liberalism are related because the one is an expression of the other. Liberalism, in Nash’s view, centers on granting rights based on intrinsic worth to the previously marginalized and defenseless. As liberal thinkers have argued for the moral consideration of more and more subjects—a process that Nash calls the “ethical extension of liberalism”—they have helped break down prejudices based on social distinctions like class, race, and gender. During the nineteenth and twentieth centuries, this ethical extension came to include all people, and then expanded its reach to nonhuman animals and, finally, the entire natural world. Environmentalism, in this schema, is the logical extension of liberal thought and the ultimate expression of liberal ethics.