Snare's puzzle/Hume's purpose: Non-cognitivism and what Hume was really up to with no-ought-from-is

In Pigden (ed.), Hume on Is and Ought. Palgrave-Macmillan (2010)
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Abstract
Frank Snare had a puzzle. Noncognitivism implies No-Ought-From-Is but No- Ought-From-Is does not imply non-cognitivism. How then can we derive non-cognitivism from No-Ought-From-Is? Via an abductive argument. If we combine non-cognitivism with the conservativeness of logic (the idea that in a valid argument the conclusion is contained in the premises), this implies No-Ought-From-Is. Hence if No-Ought-From-Is is true, we can arrive at non-cognitivism via an inference to the best explanation. With prescriptivism we can make this argument more precise. I develop an account of imperative consequence that underwrites Hare’s principle that you cannot derive imperatives from indicatives. Thus if moral judgments contain an imperative component, it will be impossible to derive moral conclusions from indicative or non-moral premises. Given this account of imperative consequence, we can explain No-Ought-From-Is without appealing to anything as nebulous as the conservativeness of logic. Hence if No-Ought-From-Is is true, we have an inference to the best explanation for prescriptivism. Both lines of argument face problems from Prior. Given Prior’s counterexamples, No-Ought-From-Is as originally conceived is false. The version that survives is No-Non-Vacuous-Ought-From-Is. But the best explanation of this does not include non-cognitivism. With prescriptivism it is worse. For the version of No-Ought-From-Is that prescriptivism ‘explains’ – that is, the version of No-Ought-From-Is that prescriptivism implies – would exclude Prior’s counter-examples to Autonomy as invalid. But they are not invalid. Thus Prior’s counter-examples to No-Ought-From- Is refute prescriptivism. Thus from 1960 onwards R. M.Hare was a dead philosopher walking. But if non-cognitivism cannot be derived from No-Ought-From-Is, this suggests that it is not what Hume was trying to prove. I argue that what Hume was trying to prove is that moral truths are not demonstrable. To be demonstrable, a proposition must be either self-evident or logically derivable from self-evident propositions. By Treatise 3.1.1.27, Hume had proved to his own satisfaction that no moral propositions are self-evident. That leaves open the possibility that they are logically derivable from self-evident but NON-moral propositions. The point of No-Ought-From-Is was to exclude this possibility. If you cannot logically derive moral conclusions from non-moral premises, you cannot demonstrate the truths of morality by deriving them from self-evident but NON-moral truths. I also discuss why Hume abandoned No-Ought-From-Is in the EPM. He had no need of it since he thought he had a proof that (with some exceptions) no nontrivial truths are demonstrable. Hence no non-trivial MORAL truths are demonstrable. No-Ought-From-Is drops out as unnecessary.
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Moral Metaphysics.Star, Daniel

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