 Mackie famously argued for a form of nihilism about morality – or, in contemporary terms, “moral error theory” – in his 1977 book Ethics: Inventing Right and Wrong. Mackie thought that there are no moral facts – or, as it will be convenient to talk about things here, that all moral claims are false. Mackie was not the first to think this, or something similar – see Olson (2014: chs. 2–4) for some of the pre-Mackie history of the view. We focus on Mackie’s argument just because it has informed so much of the last several decades of thinking about moral (and normative) error theory.