Neta’s leading idea is that descriptive facts – practices – can alone provide a full account of normativity. He first argues that, in all normative domains, descriptive facts in part determine the content of the norms, and the relevant determination relation is rational determination. Next, he tries to show that a full account of moral norms need appeal only to descriptive facts. In particular, he offers a purported account of the wrongness of promise breaking entirely in terms of descriptive facts. He concludes that it does not follow from the fact that rational determination is the relevant determination relation that normative facts must play a role. Neta also gives a purported counterexample in the legal domain – a case in which he claims that descriptive facts can themselves rationally determine the content of the law.

I begin by addressing Neta’s attempts to show that descriptive facts can alone determine norms in the moral and legal domains. First (section 2), Neta’s account of why it is wrong to break promises fails. It begs the question by taking for granted that a person’s desires or other motivational states necessarily justify the actions that they motivate. Second (section 3), Neta’s alleged legal counterexample has similar defects. Finally, in section 4, I turn to the larger issue of how far my argument applies to other normative domains.