 In contrast, it is by no means clear why mental properties would weakly supervene on physical properties without strongly supervening on them; and the analogous question arises for moral properties and nonmoral properties. Davidson and Hare owe us an explanation of why mental and moral properties weakly supervene, respectively, on physical and nonmoral ones—and it must be an explanation that does not entail that strong supervenience holds as well. Simon Blackburn’s well-known argument against moral realism basically constitutes an attempt to answer this question for Hare. Though Blackburn speaks of ‘supervenience’ and ‘necessitation’ rather than weak and strong supervenience, his argument against moral realism rests on exactly the demand for explanation that we have been exploring. He claims, 1) that moral properties weakly supervene on nonmoral properties, but do not strongly supervene on them, 2) that this requires explanation, and 3) that projectivists can do this better than moral realists (1973, 1985.) We are content to note that some such answer is required from anyone who holds a weak supervenience thesis without the corresponding strong supervenience thesis.