Role Functions, Mechanisms, and Hierarchy Author(s): Carl F. Craver Source: Philosophy of Science, Vol. 68, No. 1 (Mar., 2001), pp. 53-74 Published by: The University of Chicago Press on behalf of the Philosophy of Science Association Stable URL: http://www.jstor.org/stable/3081024 . Accessed: 07/10/2011 12:46 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. The University of Chicago Press and Philosophy of Science Association are collaborating with JSTOR to digitize, preserve and extend access to Philosophy of Science. http://www.jstor.org Role Functions,Mechanisms, and Hierarchy* Carl F. Cravertt Departmentof Philosophy FloridaInternational University Many areas of science develop by discoveringmechanisms and role functions. Cum- mins' (1975) analysis of role functions-according to which an item's role function is a capacity of that item that appearsin an analytic explanationof the capacity of some containing system-captures one important sense of "function" in the biological sci- ences and elsewhere.Here I synthesizeCummins' account with recent work on mech- anisms and causal/mechanicalexplanation. The synthesis produces an analysis of specificallymechanistic role functions, one that uses the characteristicactive, spatial, temporal, and hierarchicalorganization of mechanismsto add precision and content to Cummins'original suggestion. This synthesis also shows why the discovery of role functions is a scientificachievement. Discovering a role function (i) contributesto the interlevelintegration of multilevel mechanisms,and (ii) provides a unique, contextual variety of causal/mechanicalexplanation. *Received June 2000; revised October 2000. tSend requestsfor reprintsto the author, Departmentof Philosophy, Florida Interna- tional University, 3000 Northeast 151 Street,North Miami, FL 33181-3000;craverc@ fiu.edu. $Thanksto Ron Amundson, Robert Cummins,Lindley Darden, MichaelDevitt, Stuart Glennan, Peter Machamer, Karen Neander, Greg Morgan, Pierre Poirier, Gualtiero Piccinini,Wesley Salmon, Ken Schaffner,Steven Small, Wendy Stuart,Nathan Urban, Marcel Weber, William Wimsatt, and KirstenWood for comments on earlierdrafts of this much reworkedpaper. Thanks also to the students in Darden's graduateseminar (Fall 1998) in the Philosophy of Biology for useful feedbackon multiple drafts. Many of these friends and colleagues will not recognize this as the paper that they so gener- ously read. Any mistakes are mine and mine alone. This work was supportedby the National Science Foundation under grant number SBR-9817942.Any opinions, find- ings and conclusions or recommendationsexpressed in this material are those of the author and do not necessarilyreflect those of the National Science Foundation. Philosophy of Science, 68 (March 2001) pp. 53-74. 0031-8248/2001/6801-0004$2.00 Copyright 2001 by the Philosophy of Science Association. All rights reserved. 53 54 CARL F. CRAVER 1. Introduction.Many areas of science(and especiallythe biologicalsci- ences)develop by discoveringmechanisms and the role functionsof their components.Promises of understandingthe mechanismsof, for example, development,disease, and cognitionare coupled with claims to havefound the roles of variousgenes, cell types, and brainregions. Yet philosophers have said surprisinglylittle about how one discoversan item'srole, about why sucha discoveryis a majorscientific achievement, or abouthow these mechanisticand functionaldescriptions are related. Most of what has been said about role functionsin the philosophyof sciencehas been said by Cummins(1975, 1983),whose position is often repeatedand rarelyrevised. Cummins' account highlights the conceptual interdependenceof role functionsand what he calls an "analyticexplan- atory strategy"of understandingthe capacitiesof systemsby analyzing them into the capacitiesof theircomponents. Here I explorethe possibil- ities and consequencesof synthesizingCummins' account of rolefunctions with recentwork on the natureof mechanismsand causal/mechanicalex- planation.The synthesisyields a moredetailed analysis of properlymecha- nisticrole functionsand of the empiricalcriteria by whichmechanistic role ascriptionsare evaluated.This synthesisalso shows why the discoveryof a mechanisticrole is a majorscientific achievement. It is an achievement, first, becausediscovering an item's mechanisticrole is one way of inte- gratingit into a multilevelmechanism and, second, becauseintegration into a higher-levelmechanism constitutes a unique,contextual variety of causal/mechanicalexplanation. The argumentativestructure of the paperis as follows. In Section2, I reviewCummins' (1975) "analytic account" of rolefunctions, emphasizing as he did the connectionbetween functional ascription and analyticex- planation.In Section3, I discussthe characterof mechanismsand, most importantly,their active, spatial, and temporalorganization. I then use these aspectsof mechanisticorganization to specify-more preciselythan Cumminscould-what one assertsof an item in ascribingit a mechanistic role function. This understandingof the content of mechanisticrole as- criptionshighlights the diversekinds of evidenceby which mechanistic role ascriptionsare evaluated.In Section4, I distinguishcontextual, iso- lated, and constitutivedescriptions of an item's activity in a multilevel mechanism.It is by elaboratingand aligningthese differentkinds of de- scription,I suggest,that the levels in multilevelhierarchies are integrated together.In Section5, I introducethe possibilityof contextualmechanistic explanationas a uniquevariety of causal/mechanicalexplanation, and I respondto some criticismsof this suggestion. 2. Cumminson AnalyticExplanation and Role Functions.Cummins' (1975) analysis of function-ascribingstatements is now the canonical account ROLE FUNCTIONS, MECHANISMS,AND HIERARCHY 55 of role functions. Cummins'"regimented reconstruction" of function- ascribingstatements is as follows: X functionsas a 4)in S (or the functionof X in S is to >)relative to an analyticaccount A of S's capacityto Wjust in case X is capableof 4<-ingin S and A appropriatelyand adequatelyaccounts for S's capacityto v by, in part, appealingto the capacityof X to 4) in S. (1975, 190) Here, S is a systemwith the capacityto W,and X is a componentof S that has the capacity to 4<.Cummins does not explicatethe relationshipbe- tween S and X, but we can assumethat Xs are intendedas at least mer- eological parts of Ss. (Rescher1955) The relationshipbetween S's i-ing and the 4)-ingof Xs (diagrammedin Figure l(a)) has traditionallybeen illustratedwith the exampleof the heart and the circulatorysystem (dia- grammedin Figure l(b)). So followingtradition': The heart (X) functionsas a blood pump (4>) in the circulatorysystem (S) relativeto an analytic account (A) of the circulatorysystem's (S's) capacityto deliveroxygen and caloriesto body tissues(v) just in case the heart (X) is capableof pumpingblood (+-ing) in the circulatorysystem (S), and the analyticaccount (A) appropriately and adequatelyaccounts for the ability of the circulatorysystem (S) to deliveroxygen and caloriesto body tissues (v) in part by appeal to the capacityof the heart(X) to pumpblood (4))within the circulatorysystem (S). The clarityof Cummins'regimented reconstruction turns on the clar- ity of his understandingof systems,of the system/componentrelationship, and of analyticexplanations. Analyticaccounts (A) are explanations.They explainby analyzingthe capacitiesof systemsinto the capacitiesof theircomponent parts. System S's capacityto \y is explainedby analyzingS into the parts {X,, X2,..., Xm} and capacities {b+1,+2, . ., 4>n} relevant to S's capacity to W.Analytic explanationsexplain by showing the v-ing of S to be "reducedto the programmedexercise of the analyzingsubcapacities." By "programmed" Cumminsmeans, "organized in a way that could be specifiedin a program (or flow diagram)."(1983, 100) So the circulatorysystem's (S's) capacity to delivergoods to body tissues (W)is explainedby decomposingit into its parts (e.g., hearts (X,), arteries (X2), kidneys (X3), and valves (X4)) and capacities (e.g., to pump (4)), to convey (4)), to filter (43), and 1. The central findings of the present essay were originallydeveloped in the context of an example from contemporaryneuroscience (specifically, the LTP-Learninghypoth- esis). The example of the circulatory system is far more familiar and less confusing. This simplifiedanalysis of a familiar case can nonetheless be applied to more compli- cated cases, like the role functions of genes, pathogens, and brain regions. 56 CARL F. CRAVER a) /F b) I"_..uiIE Figure1. Relationbetween system S's x-ing and the 4>-ingof Xs, representedabstractly in (a) and appliedin the case of the circulatorysystem in (b). to regulatethe directionof blood flow (>4)) and linking those parts to- getherin the programmedy-ing of the circulatorysystem. Cumminsemphasizes that not all analyticexplanations are interesting. An analyticaccount of S's x-ing is explanatorilyinteresting only to the extentthat: (C1) The analyzing capacities {1>, >, ... , n} are "less sophisti- cated"than the analyzedcapacity