Assuming you are an atheist, cognitivist, and a moral objectivist, does Hume's Is-Ought Thesis imply you must be a moral nihilist (or perhaps more weakly, at least a moral skepticist)?

Put another way, how would a non-religious moral realist reconcile with Hume's Is-Ought Thesis? Where does their moral "ground truth" come from to begin with?

  • No. One can hold that in addition to facts ("ises") there is a different type of objective input, moral values or imperatives, the "oughts". In that case we will have objective basic "oughts", which combined with "ises" will entail other oughts without any violation of Hume's thesis. The simplest model of this sort has God as a law-giver. In addition to establishing a world order ("facts") God gives creatures room, and free will, to choose, but also commands restrictions on their choices (without compelling them). There are also secular models with objective values. – Conifold Jun 4 '20 at 3:55
  • Beyond the religious "God as law-giver" theories - what are some of the secular models with objective values and where do they find their moral ground truth? – Some Guy Jun 4 '20 at 6:29
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    See SEP, Moral Realism. For example, Aristotle's idea of "second nature" that grounds purpose and values for human beings has been modernized and defended by McDowell recently. – Conifold Jun 4 '20 at 6:44
  • Hume's thesis should be judged as neutral to morality, gap doesn't imply any end of the possible spectrum, only implies suspension for a while... – Double Knot Apr 20 at 19:16

On the moral epistemology side, one view is that we can know basic moral beliefs by moral intuition, called Ethical Intuitionism. For example, Michael Huemer's Ethical Intuitionism (2005). This can be a form of foundationalism, where moral intuition constitutes non-inferential justification for moral beliefs, a moral sense of sorts. If this is correct, then Hume's is-ought thesis is simply irrelevant, as we do not need to derive moral truths from descriptive truths.

There are also some fun logic tricks you can play to at least partially get around Hume's law. For example, a disjunction introduction of the form: A, therefore, A or B, where B is an ought. For example, the sky is blue. Therefore, the sky is blue or I ought to go punch my roommate. These are fun but do not really get fully moral conclusions based on fully descriptive premises. You can run similar examples with stuff like the paradox of material conditional or "All xs are ys. If xs ought to A, then ys ought to A."

When it comes to moral ontology, probably the most extensive defense of an explicitly atheist moral metaethic is Erik Wielenberg's Robust Ethics: The Metaphysics and Epistemology of Godless Normative Realism, a view sometimes called moral Platonism since it affirms abstract objects of moral significance. You can watch a debate between Wielenberg and William Lane Craig on the topic or read their book that came out as a result of the debate (with additional commentaries) A Debate on God and Morality: What is the Best Account of Objective Moral Values and Duties?

Finally, many of the arguments for moral realism/objectivism do not contain God in their premises, so atheist ethicists have no problem affirming that there are objective moral truths. (Note that moral realism/objectivism typically includes the rejection of error theory built in, so they affirm there is at least some objective moral truths and thus nihilism is false). Some arguments would be Terence Cuneo's (and many other's) companions in guilt arguments, David Enoch's indispensibility argument, Michael Huemer's ontological argument, etc. Also, I know there also have been specific arguments against the idea that morality has or needs a "source," but I am not that familiar.

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