 In contrast, an account of theory reduction such as the Nagel-Schaffner approach is committed to deducing a description of the higher level phenomenon from purely molecular premises. In order to deduce even a single higher level statement (a fortiori a total higher level theory on Schaffner’s account), the premises must contain (in addition to the lower level laws) a specification of the total lower level context—every feature that has some causal impact. This includes features internal to an organism and some parts of its environment. While explanatory reduction can appeal to particular causes relative to a background that is not molecularly specified, a logical deduction (as required by theory reduction) can go through only if the total causal context is contained in the  premises.[9]  A molecular characterization of the total context is in principle possible due to ontological reduction: for any higher level state there is always a total molecular configuration that determines this higher level phenomenon. However, this entails a retreat to the “in principle” possibility of a molecular derivation; not only is a molecular specification of the total context currently unavailable but it may not be forthcoming in the future (Hull 1972, 1974,  1976).[10]  In this respect accounts of explanatory reduction have a clear advantage over models of theory reduction because the former are committed neither to formal derivation nor the assumption that the explanans of the reductive explanation involves only molecularly characterized notions.