Moral non-naturalism has had something of a revival in recent years, with defenders including Russ Shaffer-Landau (2003), Ralph Wedgwood (2007), Derek Parfit (2011) and David Enoch (2011). Still, the challenge of accounting for our access to non-natural moral facts remains, and it is debatable whether any of these writers has found a satisfactory alternative to a causally problematic faculty of intuition. Perhaps the most developed suggestion is Enoch’s (2011) appeal to the indispensability of non-natural moral facts to moral reasoning, a line of argument that is analogous to Hilary Putnam’s case for non-natural mathematical objects, to be discussed in the next section below. But Enoch’s appeal arguably faces many of the same general objections as Putnam’s argument, as well as objections specific to the moral realm (see Leng 2016).