  At the beginning of the 20th Century, G. E. Moore’s open question argument convinced many philosophers that moral statements were not equivalent to statements made using non-moral or descriptive terms. For any non-moral description of an action or object it seemed that competent speakers could without confusion doubt that the action or object was appropriately characterized using a moral term such as ‘good’ or ‘right’. The question of whether the action or object so described was good or right was always open, even to competent speakers. Furthermore, in the absence of any systematic theory to explain the possibility of synthetic as opposed to analytic identity claims, many were convinced that this showed that moral properties could not be identified with any natural (or supernatural) properties. Thus Moore and others concluded that moral properties such as goodness were irreducible sui generis properties, not identical to natural properties (Moore 1903, 15). 