Abstract
Although Spinoza disagrees with Descartes's claim that animals are mindless, he holds that we may nevertheless treat them as we please because their natures are different from human nature. Margaret Wilson has questioned the validity of Spinoza's argument, since it is not clear why differences in nature should imply differences in ethical status. In this paper, I propose a new interpretation of Spinoza's argument that responds to Wilson's challenge. We have ethical commitments to other humans only because we share the same nature, for this implies that in helping them become more perfect, we also make them more useful to us. However, since animals have different natures than we do, helping them perfect themselves may make them less useful to us. Reason dictates only what it can dictate unconditionally, so it does not guide us to pursue the good of lower animals. Though Spinoza's argument is valid, there is little reason to think it sound; I conclude with a brief criticism of Spinoza's doctrine of human nature, which plays a central role in the argument.