Principia Ethica features at least two formulations of the Open Question Argument (OQA), each of which invokes ordinary intuitions about the irreducibility in content and reference of ethical vocabulary into purely descriptive vocabulary in support of the conclusion that ‘good’ is not identical to any descriptive predicate. G. E. Moore used a simple label “naturalistic ethics” for what is in fact a broad family of meta-ethical doctrines. He touched hardly at all on the big divisions within that family separating varieties of naturalism in ethics according to whether they qualify as forms of cognitivism or non-cognitivism, realism or anti-realism, and semantical or metaphysical naturalism. Frank Jackson’s analytical descriptivism, a present-day form of semantical naturalistic realism, rests on two core claims, each of which is vulnerable to the OQA. Non-reductive ethical naturalists can reply to Moore that his OQA is invalid since it draws conclusion about the nature of ethical properties from premises about the concepts expressed by some ethical and descriptivepredicates.