Ethical naturalism is the doctrine that moral properties, such as moral goodness, justice, rightness, wrongness, and the like, are among the “natural” properties that things can have. It is the doctrine that moral properties are “natural” and that morality is in this sense an aspect of “nature.” Accordingly, it is a view about the semantics and metaphysics of moral discourse. For example, a utilitarian naturalist might propose that wrongness is the property an action could have of being such as to (...) undermine overall happiness, where happiness is taken to be a psychological property. Unfortunately, it is unclear what the naturalist means by a “natural” property. For my purposes in this paper, I shall assume that natural properties are such that our knowledge of them is fundamentally empirical, grounded in observation. More precisely, a property is “natural” just in case any synthetic proposition about its instantiation can be known onlya posteriori,or with the aid of experience. (shrink)