Meta-ethics has always accompanied philosophical ethics, but in this explicit sense it came to the fore with G.E. Moore's Principia Ethica from 1903. In it he first wrote about what he called the naturalistic fallacy. Moore was seen to reject naturalism in ethics, in his Open Question Argument. This made thinkers look again at second order questions about ethics. Earlier, the Scottish philosopher David Hume had put forward a similar view on the difference between facts and values