A Role for Generalization

artifacts; machine carries the connotation of a made object, and some object to referring to living things as machines. Second, the term machine refers to the thing in the world, qua physical object. It makes sense to say things like that the machine is made of metal, the machine weighs 40 kg, or the machine just went out for repairs. As I understand it, a

mechanism is not the thing in the world qua particular object, but rather the thing in the world insofar as it operates in a particular way to perform a particular function or task.

As noted earlier in the examples of wheels and axles and gyroscopes, even prototypical mechanisms depend on more than just causescc _{for their explanations, and this is also true}

for mechanisms in the cognitive and neurosciences. Mechanistic explanations depend also on general principles, mathematical facts, laws of nature, as well as rules of less than general applicability. It is understandable that accounts of mechanistic explanation, and in partic- ular the MDC account, have de-emphasized the role of these sorts of generalizations, since mechanisms are a response to the DN account’s failure to work in the biological sciences. But if we’re to allow for type mechanisms, and if we’re to heed the norm of explanatory relevance, then some role for generalization needs to be brought back into the picture.

There are ways in which the entities and activities constituting things in the world in virtue of their organization (i.e., mechanisms) make things so, that are not causalcc. Round- ness doesn’t causecc _{rolling, having mass doesn’t cause}cc _{gravitational forces, the square of}

the hypotenuse doesn’t causecc the sum of the squares of the other two sides to equal it, but nevertheless, this sort of making things so does contribute to explanations of phenomena, and does so in a way that fits the definition of mechanism. Even if these ways of making so aren’t causescc_{, they are certainly important to how mechanisms work. In Woodward’s}

(2005) terms, they are difference-makers.

In the section on schema instantiation, we saw that Darden argues for the importance of finding “recurrent motifs” (Darden 2002), and drawing connections between different theo- ries and phenomena, but not as with Kitcher for the sake of unification as a goal in itself. Instead unifying phenomena through mechanism schemas is presented as a way of represent- ing general knowledge, and as a tool for generating hypotheses and discovering mechanisms. Skipper (1999) has similar ideas about expanding Kitcher’s notion of argument schemata to mechanism schemata. He sees “explanatory unification as proceeding via mechanism schemata, in which unificatory explanations are schematized causal mechanisms” (Skipper 1999). His paper explores

whether unification can be conceived of as the reduction of types of mechanism scientists must accept as targets of their theories and explanations, and whether it proceeds through the delineation of pervasive causal mechanisms via mechanism schemata (Skipper 1999).

In Skipper’s system, mechanism schemata explain general phenomena like selection. I think this is almost correct.

As Weber and Bouwel (2009) point out, Skipper-style unification “consists in showing that the mechanisms which lead to different events contain similar causal factors.” They go on to conclude that “This does not require subsumption under a law, so this kind of unification does not proceed by constructing arguments and showing that the events could be expected” (Weber and Bouwel 2009). But Skipper’s unification does consist in constructing arguments, even if they do not involve laws. His general mechanism schema for selection sets out an argument structure, and instructions for instantiating the variables in that structure. I am not looking for mechanistic explanations of general phenomena that just show that mechanisms leading to different events share common causal factors. What I’m looking for are mechanistic explanations that are the common factors leading to different events. If it is things in the world that explain, then mechanism schemas can’t do the job. What is needed are in-the-world analogues to schemas.

In a very recent paper, Levy (2013) argues for the value of abstraction in explanation, focusing on the Hodgkin-Huxley model. He complains that accounts of mechanistic expla- nation miss cases where “a model is deliberately ‘sketchy’, i.e. where gaps aren’t the product of ignorance or theoretical limitations, but of an intentional strategy” (Levy 2013). I com- pletely agree, and yet I am aiming for a still more general account than Levy’s. The cases he cites as benefiting from more abstract explanations are ones where lower-level entities are treated as collections or aggregates, such that the individual details of each entity are less important to the explanation than the properties of the collective. This is just one way in which abstraction from details can be useful. In that sort of case the type to which the mechanism belongs is an aggregate of some variety. There are many other types of types beyond just aggregates.

Making space for abstraction and generalizations in mechanistic explanation is something that needs to be done. The solution I propose for making space for generalizations has several additional benefits: it upholds the norm of explanatory relevance while remaining within the framework of ontic explanation, it provides the missing connection between type and token mechanisms, and it makes space for cognitive explanations that look upwards for difference-

makers.