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 "Roughly, by a complex system I mean one made up of a large number of parts that interact in a non-simple way. In such systems, the whole is more than the sum of the parts, not in an ultimate, metaphysical sense, but in the important pragmatic sense that, given the properties of the parts and the laws of their inter-action, it is not a trivial matter to infer the properties of the whole. In the face of complexity, an in-principle reductionist may be at the same time a pragmatic holist..."

This sounds very much like the Strevens/Kiesling proposal that we looked at in 2.1.1, and suffers from at least some of the same problems (as well as a few of its own). Aside from what I flagged above as Wikipedian “weasel words,” the hierarchical proposal suffers from some of the same subjectivity issues that plagued the mereological proposal: when Simon says (for instance) that one of the key features of the right sort of hierarchical composition is “near-decomposability,” exactly what is it that’s supposed to be decomposable? Again, the hierarchical position seems to be tracking something interesting here—Simon is right to note that it seems that many complex systems have the interesting feature of being decomposable into many (somewhat less) complex subsystems, and that the interactions within each subsystem are often stronger than interactions between subsystems. This structure, Simon contends, remains strongly in view even as the subsystems themselves are decomposed into sub-subsystems. There is certainly something to this point. Interactions between (say) my liver and my heart are relatively “weak” compared to interactions that the cells of my heart (or liver) have with each other. Similarly, the interactions between the mitochondria and the Golgi body of an individual cell in my heart are stronger than the interactions between the individual cells. Or, to move up in the hierarchy, the interactions between my organs seem stronger than the interactions between my body as a whole and other individual people I encounter on my daily commute to Columbia’s campus.

Still, a problem remains. What’s the sense of “stronger” here? Just as before, it seems like

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