 In response to those critiques, some, like Schaffner and Dizadji-Bahmani et al. (2010) and Butterfield (2011a&amp;b) have developed variants of the Nagel model that retain its spirit but avoid many of the problems faced by the original. Prominent suggestions concern refinements of the logical framework in which Nagelian reduction is described (Dizadji-Bahmani, Frigg, and Hartmann (2010) and Butterfield (2011a)) as well as a relaxation of the condition that reductions must be complete. The idea is that even in physics, reductions are “most likely partial, and thus not fully systematic” (Schaffner 2012: 559). As Schaffner observed, even “almost sweeping reductions” (Schaffner 2006: 379) in physics, such as the reduction of physical optics by Maxwell’s electromagnetic theory, fail at some point. Partial reductions are conceived of as “largely completed reductions containing exceptions or failures of attempted reductions” (Schaffner 2012: 563). An interpretation of partial reductions for sciences such as biology has been developed in Schaffner (2006) and further developed by Winther (2009). His suggestion heavily draws on explanatory notions and mereological relations: In a partial reduction, the objects referred to in the explanans are parts, or a microstructure of the phenomenon to be explained. The phenomenon to be explained is a macro-object. The microstructure needs to be linked via “connectability assumptions” to the macro-object. These assumptions may suggest causal links or, in more straightforward cases, identity. Such explanations may turn out to be partial for various reasons: For example, they often do not explain all cases of the target phenomenon, the reduction base may span levels of organization, and they may fall short of straightforward derivations of the target phenomenon. Such partial reductions share important features with mechanistic explanations; for example, they are local, postulate a causal mechanism that is responsible for the occurrence of the target phenomenon, refer to constituents in the explanation, and may span different levels.