It’s rare that a debate boils down to whether the participants actually believe in good and evil. Socrates’ debates with some sophists did; so too did Abraham Lincoln’s with Stephen A. Douglas. Most do not. Those skeptical of moral reasoning usually don’t deny the good outright but claim to adhere to a “thinner” conception of it than their interlocutors. They oppose actions that cause physical harm, for instance—but not much else. Many liberals and libertarians wave away moral judgment using just these sorts of arguments.

But if the only proposition concerning human nature you can admit is that we are consenting beings, you might as well be a relativist for all the moral responsibilities you neglect. Throughout his career the late Rabbi Lord Jonathan Sacks—who served 22 years as chief rabbi of the United Hebrew Congregations of the British Commonwealth and taught for years at the London School of Jewish Studies—rejected arguments that presuppose radical autonomy on the grounds that they necessitate in advance a denial of morality. He returns to this point in his last general-audience book, Morality: Restoring the Common Good in Divided Times, published shortly before his death in November.

Sacks notes that his doctoral supervisor, the English philosopher Bernard Williams, also wrote a book titled Morality (1972), in which he argued

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