It has been argued that most truths about macroscopic states of affairs are entailed by a (hypothetical) complete descriptionPof the world in microscopic terms. In principle, micro-reductive explanations of non-microphysical truths could be constructeda priori.Against this claim, I show that reductive explanation requires knowledge about the phenomena to be reduced which cannot bea prioriextracted from microphysical information alone. Such reductions proceed in two steps: a “reductionR0” (“role-occupant”) establishes that a macroproperty M plays a certain causal role (specified in macro-terms), while (...) a “reductionMM” (“micro-macro”) establishes that some microproperty gives rise toM. (shrink)