  Since non-cognitivism is a species of irrealism about ethics, it should be unsurprising that many of its main motivations overlap with those for other versions of ethical irrealism, especially with those for error theories. Early non-cognitivists seem most concerned to defend metaphysical and epistemic commitments incompatible with a realist interpretation of moral claims. For example, moral judgments seem to be empirically under-determined (Ayer 1952, 106; Mackie 1977, 39). Hence they fail tests for meaningful discourse proposed by logical positivists. If moral language is meaningful, it would be a counter-example to the view. Thus early versions of non-cognitivism were proposed by these theorists, not so much because they were interested in moral philosophy but rather to render innocuous a seeming counter-example to their own theories (Carnap 1937, 24–27; Ayer 1952, 107–109). 