Studies in History

Stud. Hist. Phil. Sci. 37 (2006) 76–80

www.elsevier.com/locate/shpsa

and Philosophyof Science

Discussion

Function, structure, capacity

Stephen Mumford

Department of Philosophy, University of Nottingham, University Park, Nottingham NG7 2RD, UK

1. Introduction

Vermaas (2006, and with Houkes, 2006) advances a ‘functions first’ or use plan viewof technical artefacts: the ICE-theory. In the theory, ‘the description of the use of arte-facts comes conceptually before the description of the artefacts themselves’ (Vermaas,2006). The engineering view puts structure first and seeks a description of an artefactin purely physicochemical structural terms, free from the psychological and sociologicalinvolvement of the use plan. For this idealised engineer, the functions of artefacts arehad solely in virtue of physicochemical structure without having to consider purposeand use. Vermaas finds a degree of reconciliation between the ICE-theory and the engi-neering view; but only a degree. Engineers can consider the structure of an artefact andsay what function a component plays in that structure. But they cannot do this for anartefact that is not part of a bigger artefact. We can know the function of an artefactas a whole only by considering the goals for which agents use the artefact and theagents’ actions. The engineering view does not provide a full theory of functions, there-fore, while the ICE-theory, according to Vermaas’s argument, does. Consequently, engi-neering cannot be a solely physicochemical enterprise. Engineers must, ultimately,consider the use plan for the artefact. The pure engineering view is incomplete, there-fore, while the ICE-theory looks sufficient to cover all cases of functional ascription totechnical artefacts.

This far I agree with Vermaas. There are, however, a number of unresolved issues in theunderlying metaphysic that may require further examination. These concern primarily therelations between structure and function and between function and capacity. Consider-ation of the structure–function distinction produces a negative for the engineering viewas described by Vermaas, I claim. Consideration of the function–capacity distinction, how-ever, produces a negative for the ICE-theory.

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2. Structure and function

The engineering view, as it is represented by Vermaas, suggests a world in which thereare both structures and laws of nature that, when taken together, can produce capacitiesand then the functions of things. This can be found in the following characterisations: ‘Forengineers the laws of physics and chemistry determine what capacities components have invirtue of their physicochemical structure, and the laws of physics determine how thecapacities of these components yield capacities of the artefact as a whole’ and ‘whether. . . buildings stay erect depends, for engineers, on the configuration of the concrete struc-ture and the laws of mechanics’.

This raises two separate questions. First, is the engineering view, so characterised, aplausible account of how the world works and of how structure relates to function? Thesecond question is whether Vermaas is offering an accurate and fair representation ofthe engineering view. I only attempt to answer the first question here and my answer is thatthe engineering view before us is an implausible account of the nature of the world. Under-standing why it is implausible will throw some illumination on the putative structure–func-tion distinction.

The idea that nature contains building blocks that are essentially causally inert, andwhich then have their actions governed or determined by the laws of nature, is metaphys-ically pervasive and clearly manifested in this version of the engineering view. The originof the idea is hard to pinpoint (see Ruby, 1986). However, Hume’s influential thesis thatthere are no necessary connections between distinct existences is highly pertinent. Such dis-tinct existences would be ideal component parts of the structure that composes an artefact.If there are no intrinsic necessary connections between distinct existences then, for post-Humeans who think that there is some necessity in the world, such necessity will haveto be extrinsic and external to those existences. This is where the notion of a law of naturemight come in. A law is a form of external necessity that is imposed on an otherwise caus-ally inert and unconnected world. The laws of nature stand apart from the building blocksbut determine their actions in the same way that legal and moral laws bind the behaviourof persons. Like the legal laws, at least, the laws of nature are typically thought to be con-tingent in that they could have been different. Once they are in place, however, they deter-mine or necessitate what will happen to things. The position is neo-Humean in thatalthough Hume denied all necessary connections, which would have to include laws of nat-ure, the position is built on Hume’s metaphysical base of a world of intrinsically uncon-nected particulars. As Lewis articulated this Humean base, ‘the world is a vast mosaicof local matters of particular fact, just one little thing and then another’ (Lewis, 1986,p. ix). Commitment to laws preserves the base but adds on necessary connections externalto the distinct existences.

This neo-Humean view, according to some recent attacks, has little to recommend it. Inthe first place, it is difficult to understand what such laws of nature are supposed to be andhow they are to govern or determine the behaviour of the world’s other elements. ‘Law ofnature’ sounds like pure metaphor, for would anyone other than a theist think that theworld’s particulars are literally controlled by external laws? But in the second place, wouldany such laws be needed? Only, it seems, if the world is essentially inanimate and uncon-nected otherwise. For realists about causal powers or capacities, ours is not such a world(Ellis, 2001). Real causal powers would provide an anti-Humeanmetaphysic, with necessaryconnections between distinct existences but which were internal to the distinct existences.

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Despite these connections being necessary, I needn’t be able to know them a priori. Hence Iwould need some scientific knowledge to know what functions attach to what structures.There can be necessary connections between distinct existences, however, even if they areknowable only a posteriori (Kripke, 1980). If there are such connections, then laws of natureare metaphysically redundant (Mumford, 2004). The engineering view, as Vermaas presentsit, would be based on a faulty metaphysic.

What implications does this have for the structure–function distinction? Most impor-tantly, it would mean that the distinction between structure and function was a relativerather than absolute one. Hume’s idea of a world of causally inert objects would berejected. Hence the division between structures, which have no intrinsic necessary connec-tions to other things, and functions which do, would be chimerical. All of the world’s ele-ments would have intrinsic functional aspects. The notion of a structure can be retained,however, if it is suitably detached from a Humean metaphysic. A structure is most typi-cally understood as a complex of component objects. Our minimum requirements, forsomething to qualify as a structure, are multiple elements and an appropriate relationbetween them. In the case of artefacts, therefore, the elements would be the componentparts and the appropriate relation would be having the components arranged in the rightway so that the artefact is a coherent whole instead of a collection of scattered parts. Thereis no dual nature requirement in that the component parts could have the same nature—afunctional one—as the whole that they compose. Hence the structure–function distinctionmay be merely a distinction between the realiser and the realised. It need not point to adual metaphysical nature. A structure can be understood as a structure of functions, there-fore—a structure of essentially functional elements—hence not something that contrastsmetaphysically with function. Something could count as a structure only relative to ahigher-level function that it realises. But for the lower-level structures that realise it, thesame thing might count as a higher-level function. There is not necessarily a dual natureto be found here but only things of the same nature standing in different relations ofrealisation.

The main problem with the engineering view, as Vermaas sees it, is that it understandsfunctions to be a product of purely physicochemical structures and processes. It does not,therefore, take account of the plan of use for the artefact. To understand the appeal andplausibility of Vermaas’s claim, we need next to consider the distinction between functionsand capacities.

3. Function and capacity

A physical particular can have many capacities, powers or dispositions. My stapler isable to pierce paper with staples and fold them flat. But it also has a capacity to sit ontop of papers and hold them down, to reflect light of a certain wavelength, even to smasha window if I throw it in the right way. Only the first kind of capacity gets singled out asthe function of the artefact. The ICE-theory explains why it is this particular capacity,rather than the others, that is the artefact’s function. The stapler has been developedfor a use plan that makes use of this specific capacity and not, for instance, its window-breaking capacity.

The theory thus exploits an alleged distinction between function and capacity. Accord-ing to the ICE-theory, an agent believes something has a function when it has a capacitythat can be manipulated in the execution of the use plan to achieve the goal. A function,

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this suggests, is gained from having a manipulable capacity appropriate to the use plan.The function, therefore, is distinct from the capacity. It would arise from the capacity plussome other factor: the use plan that exploits it. The mistake of the engineering view, onewould assume, was to attempt an analysis in terms of capacity alone—objective and phys-icochemically explicable—without introducing the social and psychological elements ofthe use plan. Is it correct, though, that functions can be understood in terms of capacities?

There are at least four possible positions that can be held on the relation between func-tions and capacities: first, that they amount to the same thing; second, that functions canbe explained in terms of capacities; third, that capacities can be explained in terms of func-tions; fourth, that they are completely unrelated.

The first view has some appeal because what can be said of capacities can often be saidof functions just the same. A capacity can persist in a particular even if it is never mani-fested but, similarly, something may have a function that is never put to use. A can opener,for example, might never be used to open a can. Nevertheless, it still seems correct to saythat this is the can opener’s function. But Vermaas makes real progress in showing howcapacity and function, for artefacts, differ. The function persists without being put touse because the capacity to open cans persists. But the capacity alone would not be suffi-cient for the function, which is determined also by the use plan. Functions and capacitiesare not, therefore, the same thing.

Vermaas opts therefore for the second view: functions can be explained in terms ofcapacities. Here, Vermaas follows the general approach of Cummins’s influential treat-ment where one can give an account of having a function by, in part, appealing to thenotion of having a capacity (Cummins, 1975, p. 762). The problem with this view is thatone would then require an account of what a capacity was and this would have to be anaccount that did not use the same notion of function, upon danger of circularity. If thenotion of a capacity is no better understood than that of function then one could arguethat little has been gained from a capacity-based view of functions. So how might weunderstand capacities? One option is indeed a functionalist account (Mumford, 1998,Ch. 9). This account states that capacities are properties understood according to whatthey can do or what function they can play in relation to other properties. This is, then,to offer the third option: an explanation of capacities in terms of functions. It is also arejection, therefore, of the fourth option: that function and capacity are unrelated.

What recommends this view? An argument that is presented elsewhere (Mumford,1998, pp. 200–204) is that function is a more wide-ranging concept than disposition orcapacity. Hence capacities constitute a subset of functions rather than functions a subsetof capacities. Seeing the relation this way round allows that there could be things withfunctions that are not grounded in capacities. Some plausible instances of such functionsare the function of a flag to add grandeur, the function of a road sign (to slow traffic, forinstance) and the function of a rule in a game. The last example in the list shows that func-tions can be ascribed not just to artefacts, nor even just to physical objects, which showsthat functional discourse is broader than capacity discourse.

If capacities are to be understood in objective terms, as mind-independent and physico-chemically explicable, then can one really explain the function of a flag or a road sign interms of one of its capacities? The flag functions to add grandeur to an occasion or loca-tion; but does it really have a grandeur bestowing capacity or any capacity that mightexplain that grandeur? It is capable of flying in the wind and of reflecting light but thesecapacities don’t explain the function. In this case, therefore, we seem to have a function of

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an artefact in which none of its capacities play a prominent role or any role at all. Thesame can be said of road signs. They are capable of reflecting light and being seen by roadusers but this alone doesn’t explain why drivers alter their behaviour when passing them.

The explanation of such functions should no doubt involve notions of convention andintention. A road sign that says ‘frogs crossing’ is understood by me to have been inten-tionally created in line with a set of shared conventions. I understand that a flag isintended to add grandeur and intended to be understood by me as adding grandeur,but that it does so is purely a matter of convention.

Such functions are not necessarily counterexamples to the ICE-theory, which restrictsitself to technical artefacts and technical functions and does not cover symbolic or socialfunctions. The cases are meant to show, however, that function is a broader concept thancapacity. In turn this suggests that capacities might plausibly be understood as kinds offunctions rather than, in the ICE-theory, functions being understood as kinds of capaci-ties. To avoid circularity, it seems we cannot hold both a functionalist theory of capacitiesand a capacity theory of functions. The ICE-theory opts for the latter theory; I prefer theformer.

4. Conclusion

The ICE-theory no doubt provides a superior theory of functions than the idealisedengineering view. Function cannot be simply a matter of physicochemical structure.Indeed, as I have argued above, this view may rest on an unnecessarily bifurcated pictureof reality. But is an artefact’s function simply a matter of a capacity manipulated in accor-dance with a use plan? For many functions of many artefacts—the technical artefacts—this seems a plausible account. At least some of the functions of some artefacts, however,are outside the scope of the ICE-theory. I fear that there is a more general issue that isbehind this. If we cannot understand capacities independently of the notion of function,then an analysis of function in terms of capacities is either circular or incomplete.

References

Cummins, R. (1975). Functional analysis. Journal of Philosophy, 72, 741–765.Ellis, B. (2001). Scientific essentialism. Cambridge: Cambridge University Press.Kripke, S. A. (1980). Naming and necessity. Oxford: Blackwell.Lewis, D. (1986). Philosophical papers II. Oxford: Oxford University Press.Mumford, S. (1998). Dispositions. Oxford: Oxford University Press.Mumford, S. (2004). Laws in nature. London: Routledge.Ruby, J. (1986). The origins of scientific ‘‘law’’. In F. Weinert (Ed.), Laws of nature: Essays on the philosophical,

scientific and historical dimensions (pp. 289–315). Berlin: de Gruyter.Vermaas, P. E. (2006). The physical connection: Engineering function ascriptions to technical artefacts and their

components. Studies in History and Philosophy of Science, 37, this issue. DOI:10.1016/j.shpsa.2005.12.017.Vermaas, P. E., & Houkes, W. (2006). Technical functions: A drawbridge between the intentional and structural

natures of technical artefacts. Studies in History and Philosophy of Science, 37, this issue. DOI:10.1016/j.shpsa.2005.12.002.