 Other reconceptions of both reduction and the mind-brain identity theory have been proposed explicitly to handle multiple realizability. Elliott Sober (1999) insists that a reductionist thesis actually follows from the multiple realizability premise. He begins by attacking Putnam’s (1967) “objective” account of superior explanation, namely that one explanation is superior to another if the former is more general. According to Putnam, superior explanations “bring out the relevant laws”. But Sober reminds us that explanatory generalizations at lower levels bring out more details. Science “aims for depth as well as breadth” and there is no “objective rule” concerning which endeavor is “better” (1999: 550). Both reductionists and anti-reductionists err in privileging one aim at the expense of the other. Sober then notes that multiple realizability presupposes some form of asymmetric determination: the lower level physical properties that are present at a given time determine the higher level properties that are present. But this assumption commits its proponents to the causal completeness of physics, the thesis that physical effects have only physical causes (a doctrine that Sober sketches toward the end of his 1999). If one is also concerned with causal explanation—that is, if one holds that individual occurrences are explained by citing their causes—then the causal completeness of physics in turn commits multiple realizability proponents to physics’ possessing an important kind of explanatory completeness that all other sciences lack. This is “reductionism of a sort” (Sober 1999: 562).