multiple realizability intuitions

MULTIPLE REALIZABILITY INTUITIONS AND THE

FUNCTIONALIST CONCEPTION OF THE MIND

WILLIAM RAMSEY

Abstract: A popular argument supporting functionalism has been what is com-monly called the ‘‘multiple realizability’’ argument. One version of this argumentuses thought experiments designed to show that minds could be composed ofdifferent types of material. This article offers a metaphilosophical analysis of thisargument and shows that it fails to provide a strong case for functionalism. Themultiple realizability argument is best understood as an inference-to-the-best-explanation argument, whereby a functionalist account of our mental conceptsserves to explain our multiple realizability intuitions. I show that the argument isinadequate because alternative accounts of our mental concepts exist that provideequally plausible explanations for these intuitions. Moreover, in the case of ourqualia concepts, a nonfunctionalist account explains several other intuitions thatfunctionalism cannot explain. Thus, despite its popularity, the intuition-basedversion of the multiple realizability argument is a poor reason for acceptingfunctionalism.

Keywords: dualism, folk psychology, functionalism, inference to best explana-tion, intuition, mental concepts, multiple realizability, qualia, reduction, thoughtexperiments.

1. Introduction

Since its inception, the functionalist theory of the mind has been subjectedto a growing number of challenges and criticisms.1 However, in spite ofthe existence of what is, by now, a formidable collection of objections, thetheory has proven remarkably resilient. A good deal of this hardiness isdue to the influence of one line of reasoning, the ‘‘multiple realizability’’argument. This argument claims that mental states can be instantiated indifferent mediums, and that they are therefore best understood asfunctional states whose identities are determined by their causal-rela-tional properties. While functionalism may have its difficulties, itsproblems have not proven sufficiently damaging to overcome the persua-siveness of this argument. Traditionally, there have been two different

1 See, for example, Shoemaker 1975, Block 1980a, Putnam 1988, and Maudlin 1989.

r 2006 The AuthorJournal compilation r 2006 Metaphilosophy LLC and Blackwell Publishing LtdPublished by Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK, and350 Main Street, Malden, MA 02148, USAMETAPHILOSOPHYVol. 37, No. 1, January 20060026-1068

r 2006 The AuthorJournal compilation r 2006 Metaphilosophy LLC and Blackwell Publishing Ltd

types of multiple realization argument for functionalism, stemming fromtwo different sorts of evidence: alleged empirical cases of multiplerealization and thought experiments involving hypothetical scenarios.Recently, the former version of the argument has come under attack(Bechtel and Mundale 1999; Couch 2004), and it is far from clear whetherthere actually are any real cases of type-identical mental states instan-tiated by sufficiently different neural states. No problem for functional-ists. They can fall back on imaginary cases to support their claim ofmultiple realizability. In fact, it has been the imaginary cases that havetraditionally provided the strongest support for their view.

In this article, I want to focus on the alleged support that thenonempirical versions of the argument provide for functionalism.Although multiple realization has recently received considerable attention(Batterman 2000; Kim 1992; Polger 2004; Shapiro 2004), the mannerin which it supports the functionalist theory of the mind has notbeen adequately explored. My goal is to demonstrate that the thoughtexperiments, and the intuitions they reveal, do not provide a compellingcase for functionalism. In fact, I’ll suggest that with regard to animportant class of mental concepts, the multiple realizability argumentfor functionalism fares rather badly. Spelling all this out is the primaryobjective of what follows. Along the way, I hope to provide a newperspective on a number of earlier debates and criticisms surrounding thefunctionalist position.

To do all this, the article will have the following organization. In thenext section, I give what I believe is the proper interpretation of thethought-experiment-based version of the multiple realizability argument.In my reconstruction, I demonstrate that the argument is best under-stood as an inference to the best explanation that is primarily aboutthe nature of our mental concepts. Then, in section 3, I show that theargument fails because there exist plausible alternative explanations forthe way our mental concepts behave, and that at least one of these doesa far better job of accounting for other intuitions that functionalism failsto accommodate. As I develop my argument, I also try to shed newlight on a host of issues that pertain to functionalism. Section 4 offers abrief conclusion.

2. How Does Multiple Realizability Support Functionalism?

In this section I want to present the conceptual-based multiple realiz-ability argument for functionalism in its most favorable light. To do that,I need to establish two things about the argument. The first is that it ismost naturally understood as having the form of an inference to the bestexplanation. The second is that we should understand its primary andcentral conclusion to be about the nature of our mental concepts, and thatfunctionalismFqua metaphysical thesisFis actually a secondary


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conclusion that requires further argument. Since the argument is almostalways presented in a very informal manner, all of this is going to requirea fair bit of reconstruction. We can begin by briefly recounting how theissue of multiple realization typically enters into discussions about the mind.

The central claim of the nonempirical version of the multiple realiz-ability argument is simply that mental states, like beliefs or painstatesFcan be instantiated by different physical (or even nonphysical)substances. Polger (2004, 6) and Shapiro (2004, 7) identify four versionsof the multiple realizability thesis, but for our purposes the version theycall the ‘‘Standard Multiple Realizability Thesis’’ will do just fine:‘‘Systems of indefinitely (perhaps infintely) many physical compositionscan have minds like ours’’ (Shapiro 2004, 7). This claim is often defendedthrough certain thought experiments designed to illustrate its intuitiveplausibility. Here are two familiar examples:

(1) Martians have just landed. One of the creatures injures itself; itwinces and engages in the Martian equivalent of what we wouldordinarily consider to be pain behavior. Upon further investigation, welearn that the Martian’s ‘‘brain’’ has a functional architecture similar toour own, but made up of silicon. Question: Should learning that theMartian’s brain is silicon based (instead of carbon based like ours)preclude us from attributing pain to the Martian? The obvious, intuitiveanswer seems to be no.

(2) A friend has a form of progressive brain cancer that can be treatedonly by replacing diseased neurons with artificial, nonorganic devices. Inall relevant respects, the prosthetic neurons perform in a way that islargely indistinguishable from the way real neurons perform. After thefirst operation, in which only a few neurons are replaced, your friend saysshe feels normal. Unfortunately, more transplants are necessary to stopthe cancer. This keeps up for years, until your friend winds up withnothing but artificial neurons in her head. Question: Has she graduallylost her mind, becoming a nonmental zombie? Again, the obvious,intuitive answer appears to be no.

What do these thought experiments demonstrate? In terms of thesupport they provide for functionalism, they serve to establish bothnegative and positive theses. The negative thesis is that mental-state typesdo not reduce to neurological-state types. The thought experiments seemto demonstrate the implausibility of such a reduction, since they illustratethat it is intuitively possible for creatures lacking the requisite neurolo-gical make-up nevertheless to possess mental states. Consequently, thetype-identity thesisFwhich claims that types of mental states are to beidentified with types of neurological statesFis mistaken. The positivethesis is that mental-state types should instead be reduced to functionalstates. In other words, the thought experiments are generally regarded asdemonstrating that mental states are functional kinds, defined by theircausal-relational properties.


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The Argument as an Inference to the Best Explanation

It is the argument for the positive thesis that, I would like to suggest,should be understood as an inference to the best explanation (ITBE). Onthis reading, the phenomenon that needs explaining is multiple realiz-ability itselfFthe fact that it clearly seems possible for radically differentkinds of substances to realize minds. The thought experiments serve asevidence about the nature of minds and, more specifically, about thekinds of properties that are essential for mental states. If it is possible forcreatures like silicon Martians or for people with prosthetic brains topossess mental states, then mental states must not have a physical essence.That is, they are not defined by virtue of their physical or compositionalproperties, since it is possible for those properties to vary. But if thephysical or compositional properties of a pain state aren’t what make it apain state, then what sort of properties do?

Functionalism provides an answer to this question. Mental statesaren’t to be defined by virtue of their physical/compositional properties,because they are really defined by their causal/relational properties.2 Thereason we intuitively think a silicon-based Martian can have a mind, orthat a person can have her neurons replaced without becoming a zombie,is because what counts is not the stuff but what the stuff does. Themultiple instantiability of mental states is explained by the proposal thatmental states are not natural kinds, like water or gold, but functionalkinds, like doorstops or valve lifters. We find functionalism about mentalstates so plausible precisely because it seems the most obvious way ofaccounting for the multiple realizability of mental states. In certainrespects, the argument can be seen not simply as an inference to thebest explanation but as an inference to the only explanation of multiplerealizability worth taking seriously.

In defense of this reading of the multiple realizability argument, weshould note that it accommodates other ways in which multiple realiz-ability has been linked to functionalism. For example, multiple realiz-ability is sometimes treated as a direct consequence of functionalism,rather than as a premise in a supporting argument. If mental states aredefined by their causal-relational properties, then it follows that anysubstance instantiating those properties will instantiate a mind. At firstglance, this seems to challenge the idea that multiple realizability is usedto argue for functionalism, as things appear to be going the other way

2 There are, of course, a variety of different versions of functionalism (see Block 1980b).Perhaps the most significant distinction is between Putnam-style functionalism, whichidentifies mental states with functional roles, and Lewis-style functionalism, which identifiesmental states with occupants of functional roles. Still, all versions of functionalismFinclud-ing Lewis’sFare defended by appeal to multiple realizabilty thought experiments. I’m usingthe term functionalism to designate the core idea that mental states should be type identifiedby virtue of causal or relational properties.


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around. Yet, this is fully consistent with the ITBE interpretation.Abductive arguments of this sort typically involve premises that aredirectly entailed by their conclusions. Since multiple realizability is adirect consequence of functionalism, any evidence for multiple realiz-ability will count as confirming evidence for functionalism.

As we noted earlier, multiple realizability is also sometimes treatedas providing an argument against functionalism’s competitors, such asthe type-identity theory. If mental states can be instantiated in sub-stances other than neurons, then, contrary to the type-identity story,neurological states are not necessary for mentality. Consequently,the multiple realization argument rules out certain ways of characteri-zing the mind. Again, this is exactly what we should expect from anITBE argument. It provides us with disconfirming evidence againstcertain obvious alternatives to functionalism, leaving functionalismstanding as the only apparent theory that can handle this feature ofmentality.

In effect, what I am suggesting here is my own inference-to-the-best-explanation argument for the ITBE interpretation of the multiplerealizability argument. Given the above considerations, and given thatthere aren’t many other ways that multiple realizability could supportfunctionalism, the ITBE interpretation best explains the argument’slong-standing appeal. Of course, it also opens up certain avenues forchallenging the argument, such as the possibility that there are betterexplanations for multiple instantiability attitudes besides functionalism.The primary goal of this article is to convince you that such alterna-tive explanations do in fact exist. But before I do so, I want to considera different problem for the multiple realizability argument. In theprocess, I hope to be clearer about just what, exactly, the argument isan argument for.

The Role of Mental Concepts in the Argument

In the argument as presented above, it was claimed that certain thoughtexperiments demonstrate that it is possible for minds to be instantiated indifferent physical mediums. But strictly speaking, the thought experimentsonly demonstrate that it seems possible that minds could be realized indifferent mediums; they tell us something about our intuitions about themind. We have no direct evidence about what is or is not possible regardingMartian mentality or mentality associated with prosthetic brains. It isclearly one thing to demonstrate that we think silicon Martians could havemental states; it is an entirely different matter to demonstrate that they infact could. A critical question, then, is how we go from the observation thatmultiple realizations seem intuitively possible to the claim that they actuallyare possible. In other words, why should we take these intuitions seriously?Since intuitions about what is or is not possible have proven mistaken in



the past, why couldn’t someoneFa type-identity theorist, sayFclaim thatour intuitions are simply wrong on this point? How do we get metaphysicalpossibility out of mere conceivability?3

The reliability of intuitions concerning what is metaphysically possi-ble certainly cannot be taken for granted.4 Nonetheless, I think thereare strategies that can, at least initially, help us get around these worries.What I would like to do next is spell out an argument that can be usedto bridge the gap between our intuitions and the actual nature of mentalstates. While the argument is not immune to difficulties, it provides whatI take to be the most charitable interpretation of the multiple realizabilityargument.

What is needed is an argument that takes us from a psychologicalclaim about our intuitions to the metaphysical thesis that mental statesare functional kinds. Here is one way to do it:

a. Our intuitions allow the multiple realization of mental states.b. Therefore, our mental concepts permit the multiple realization of

mental states.5

c. Therefore, our mental concepts are functional concepts.d. Therefore, to exemplify a given mental concept, a state must be

type-identified by its causal-relational properties.e. Therefore, functionalism (qua metaphysical thesis about the mind) is

true.

Premise (a) is supported by thought experiments like the Martian andneural-transplant cases. Premise (b) follows from (a) and the widespreadassumption that our intuitive judgments stem from the utilization andapplication of our various concepts. The move from (b) to (c) is what Iwould now like to suggest is the proper way to understand the abductiveinference of the multiple realizability argument. Understood in this way,the explanandum of the argument shifts from multiple realizability to theintuition that multiple realizations are possible. In other words, thephenomenon that requires explanation now becomes the psychologicalfact that people intuitively think minds are multiply realizable. Theinference is to an account of how we conceive of minds. The claim isthat the best explanation for our multiple instantiation intuitions is tosuppose that our mental concepts are functional concepts. By ‘‘functional

3 Notice that the skeptical worry here is more serious than the worries we confrontregarding other sources of knowledge, such as observation. At least with observation there isa causal story to tell concerning how information is conveyed to our mind from whatever weare observing. In the case of metaphysical possibility and intuition, however, such a storydoes not appear to be available.

4 See DePaul and Ramsey 1998 for a number of discussions on this point.5 Throughout this paper I use the term concept to designate psychological entities, as

opposed to abstract entities.


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concept’’ I mean a concept in which the ‘‘slot’’ for essential properties isfilled by representations of causal-relational properties. Assumingthat our mental concepts are functional in this manner makes the linkbetween our multiple realization intuitions and a functionalist concep-tion of the mind fairly direct. The intuitions are explained as conceptualprocesses in which representations of causal-relational essences remainfixed, while representations of (contingent) physical properties arevaried. But this still leaves us with a claim about our conception of themind. How do we get beyond that to a claim about the actual nature ofthe mind itself?

To bridge that gap, premise (d) introduces conditions for conceptinstantiation. The point of (d) is to suggest that our conceptual frame-work puts severe limits on the sort of properties that could qualify asessential for mentality. If we assume that our mental concepts actually arefunctional concepts, then only causal-relational properties would qualifyas defining features of mental states. We couldn’t discover that we arewrong about this, since any other sort of demarcation strategy won’tcapture our mental notions. If someone tried to individuate a givenmental-state type by appealing to different sorts of properties, such asneurochemical properties, then we would have to sayFindeed, manyhave saidFthat the person has failed to pick out the right sort ofproperties for taxonomizing mental states. If our mental concepts treatcausal or relational properties as essential, then those causal or relationalproperties are the criterion for membership in the class of states pickedout by those concepts. It is in this way that we go from a claim about thenature of our concepts (that is, that our mental concepts are functional)to a claim about the nature of the world (that is, that mental-state kindsare functional kinds). What all of this amounts to is a sort of conceptualanalysis, but conceptual analysis pitched at a certain level of abstraction.Rather than giving actual necessary and sufficient conditions, the argu-ment instead tells of the sorts of properties that qualify as candidates fornecessary and sufficient conditions. In the case of mental states, theyaren’t intrinsic or compositional properties; instead, they are relationalproperties.

As I suggested above, it is not entirely obvious that this sort of storycan be made to work, as there are a host of problems concerning the movefrom (c) to (d). For example, there are compelling reasons for thinkingthat our conceptual frameworks are far more malleable and open torevision than the argument just given suggests. But at least we can see thatthere is an argument taking us from our multiple realizability intuitions,through a claim about our mental concepts, to a claim about the nature ofmental states. The move I want to focus upon in the remainder of thisarticle is not the inference from (c) to (d) but the abductive inference from(b) to (c)Ffrom our multiple realizability intuitions to the claim that ourmental concepts are functional concepts.



A natural way to regard the inference from (b) to (c) is to treat theintuitions as data of sorts, telling us something about the nature of theconceptual machinery that produces them. This is similar to a strategyemployed by linguists, who argue from certain linguistic intuitions tospecific claims about the nature of the cognitive apparatus used inlanguage processing. Since aspects of this apparatus are not directlyaccessible to consciousness, we can only ‘‘get at’’ them by probingintuitive judgments about different types of sentences. Similarly, whenproperly filled out, we see that the multiple realization argument is a wayof uncoveringFthrough an appeal to our intuitive judgmentsFwhatoften gets referred to as our tacit ‘‘folk’’ or ‘‘commonsense’’ psychology.

One writer who has endorsed the idea that philosophers of mind are in-vestigating mental concepts is David Armstrong, who tells us that ‘‘theconcept of a mental state essentially involves, and is exhausted by, theconcept of a state that is apt to be the cause of certain effects or apt to bethe effect of certain causes’’ (1981, 20). Not all functionalists, however,acknowledge this sort of psychologism. For example, Hilary Putnam’simportant article ‘‘The Nature of Mental States’’ goes to some length toargue that it is ‘‘discussing not what the concept of pain comes to, butwhat pain is’’ (Putnam 1975, 433). Putnam insists that since the version offunctionalism he is advancing is an ‘‘empirical hypothesis,’’ it is not, heclaims, defended on a priori grounds.

Nonetheless, even in Putnam’s functionalism as protoscience a strongappeal is made to how we would regard extraterrestrial life, intuitive waysof attributing mental states to nonhumans, and what seem to be reason-able criteria for identifying creatures with mentality. When Putnam tellsus that functionalism is superior to the identity theory because the former‘‘is more plausible,’’ it appears that what ‘‘more plausible’’ amounts tohere is agreement with our commonsense conception of the mind. So,even though Putnam insists he isn’t interested in our conception of pain, itis precisely that conception that appears to serve as an intuitive forcebehind his nonempirical versions of the multiple realizability argument.

Summary

So far we have established two important theses about the thought-experiment version of the multiple realizability argument. The first is thatthe argument’s form is best understood as an inference to the bestexplanation. The second is that the argument is at least tacitly a claimabout the nature of our mental concepts. Putting these two together, theargument says that we must adopt a functionalist interpretation of ourmental concepts (that is, a functionalist reading of folk psychology) inorder to explain our multiple realizability intuitions. It claims that func-tionalism is the best, if not the only, explanation for the intuition thatmental states could be possessed by cognitive systems made of different


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kinds of stuff. Given this reconstruction, we are now set critically toevaluate the argument.6

3. Accounting for the Multiple Realizability Intuition

The multiple realization argument is sometimes presented with thefollowing question: ‘‘How else besides functionalism could we accountfor the fact that silicon Martians (or people with prosthetic brains) couldhave minds?’’ Given our reconstruction, we should now view thisquestion as follows: ‘‘How else besides a functionalist interpretation ofour mental concepts could we account for the intuition that siliconMartians (or people with prosthetic brains) could have minds?’’ Althoughthe question is intended as rhetorical, it is the question I intend to answerhere. To get the ball rolling, I’ll first show that the functionalist account ofour mental concepts is not the only game in town by offering somealternative explanations for our multiple realizability intuitions. Then I’llsuggest one further account that explains not only our multiple realiz-ability intuitions but also a host of other intuitions that have provenembarrassing for the functionalist.

Two Alternative Hypotheses about Our Mental Concepts

Dualistic Folk Psychology. One non-functionalist account of our mentalconcepts that could possibly explain our multiple realizability intuitions isthe suggestion that our mental concepts are dualistic. On this proposal,our commonsense intuitions are driven by a deeper conception ofmental states that treats them as existing in some sort of nonphysicalform. In other words, our mental concepts behave as something like‘‘supernatural-kind’’ concepts, where mental states are defined as states ofsome yet to be discovered nonphysical substance. Such a conception mayallow brains to interact with nonphysical minds, but it would precludephysical brains from actually instantiating any sort of mental state. Onthis view, despite our enlightened theoretical beliefs, we’re all closetCartesiansFat least with regard to our intuition-generating folk theory.

To see how a dualistic folk psychology would explain multiple realiz-ability, consider our earlier examples. So long as the folk theory sanctionsmind-silicon interactionFthat is, allows the nonphysical mind to interact

6 In this section, I construe the multiple realizability argument as involving a claim aboutthe nature of our mental conceptsFthat our mental concepts are functional concepts. I dothis because it strikes me as the most charitable reading of the argument, despite itsdifficulties. Without such a claim, the link between the relevant dataFthe multiplerealizability intuitionsFand functionalism as a metaphysical thesis becomes much harderto see. I appreciate, however, that there are some philosophers who do not find theconnection between intuitions and metaphysics as troubling as I do and believe thatintuition is a highly reliable guide to the way the world is.



with silicon brains every bit as much as they interact with carbon-basedbrainsFwe’ll naturally come to think that Martians could have mentalstates. Similarly, so long as our conception allows for the nonphysical mindto reestablish causal connections with prosthetic neurons, such a conceptionwould generate the intuition that the person with a prosthetic brain retainsher mentality. In both cases, the suggestion is that agents with differentsorts of brains can nevertheless have minds, not because minds are multiplyrealizable but because deep down we think brains aren’t where the action is.That is, with the dualistic explanation, the intuitive interchangeability ofwhat’s in the head is not actually a case of multiple realization. Instead, it isa simple case where two things (mind and brain) stand in a certain relationand we recognize that by altering one of the relata (the brain) we needn’talter the other. We think carbon-based neurons are irrelevant for mentality,because they never, intuitively, housed mental states in the first place.

One distinctive advantage of the dualistic theory of our mentalconcepts is that it has considerable independent support, apart from itsability to explain multiple realizability intuitions. For example, peopleoften express a sincere belief in out-of-body existence both before andafter death. This is typically supported by an appeal to the existence ofsome sort of nonphysical spirit or soul that serves as the seat of mentality.There is also some degree of psychological evidence for this view. Forexample, developmental psychologist Henry Wellman tells us that‘‘young children are dualists: knowledgeable of mental states and entitiesas ontologically distinct from physical objects and real events’’ (1990, 50).It seems, in our culture at least, that a fairly strong case could be made forthe thesis that our primordial folk psychology is one that regards theontology of the mind as essentially nonphysical.7

Mental Cluster Concepts. A second alternative to functionalism inexplaining our multiple realizability intuitions is the possibility that ourmental concepts are actually disjunctive cluster concepts, admitting of nosingle defining essence.8 On this view, our mental concepts are inherentlydisjunctive; there isn’t any further fact that explains why they aredisjunctiveFthey just are. Thus, mental concepts would have the formof what Wittgenstein once referred to as a sort of ‘‘family-resemblance’’structure, with no unique set of defining properties. As Wittgenstein

7 It should be emphasized that the advocate of the view suggested here is in no waycommitted to the metaphysical truth of dualism. Instead, the claim is about the tacitconceptual framework that drives our intuitive judgments about mentality. It is worth notingthat even for those of us who consciously reject dualism a more primitive dualisticconception of the mind may nevertheless influence our deeper intuitive judgments. Somestudies in cognitive research suggest that a more rudimentary conception can influenceintuitive judgments even after considerable training and education has been directed againstit (see McCloskey 1983 and Clement 1983).

8 This possibility was first pointed out to me by David Armstrong.


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noted, our concept of ‘‘game’’ seems to have this feature, where it isimpossible to construct or discover any single set of essential properties.Our notion of a game is multiply realizable not because it is a functionalconcept (games have too many diverse functions) but simply because theconcept involves a very broad range of only partially overlappingcharacteristics.

If mental concepts are like our notion of a game, then we would haveanother explanation for the intuitive multiple realizability of mentalstates. It would not be because our mental notions have a functionalessence but because they have no essence. If mental concepts have thisform, it would generate the intuition that very different things couldqualify as mental states in different contexts. Pain in a human wouldbe one type of pain, whereas pain in a silicon-based Martian would be justa different type of pain. The two cases would both count as instantiationsof our pain concept, not because they share some single set of causal-relational properties but simply because they possess some of the diversefeatures that are sufficient to produce the intuition that pain is instan-tiated. In fact, if our concept is wildly disjunctive the two instancesneedn’t even share any features. They might, for example, simply besufficiently close to a central prototype to intuitively qualify as examplesof pain.

As with the dualistic theory, this way of accounting for the multiplerealizability intuitions has a fair amount of independent support. Sincethe work of Eleanor Rosch on categorization judgments (Rosch 1973 and1978), most psychologists have abandoned the classical view that ourconcepts have a ‘‘defining essence.’’ In place of the classical view, research-ers have adopted different versions of a ‘‘prototype’’ theory of concep-tual structure, a theory not far from the one suggested by Wittgenstein.According to some of the more popular versions of this account, intuitiveinstances of a given category can be highly heterogeneous in their make-up. If such a theory should prove correct with regard to our mentalconcepts, it would provide us with a nonfunctionalist explanation for themultiple realizability intuitions.

A Functionalist Reply

By now I hope it is clear that a functionalist theory of our mental conceptsis not the only way to account for the intuition that mental states can beassociated with radically different types of brains. There are otheraccounts of our mental concepts that also account for those intuitions,and we have some independent reasons for thinking that those alternativetheories might be correct. In response to all this, the defender of function-alism might reply in the following manner. Sure, it might be admitted thatif we look only at the multiple realizability intuitions, there appear to beother explanations available. But as with most ITBE arguments, it was



never claimed that we should take into consideration only those intuitions.The original claim was that functionalism provides the best explana-tion, all things considered. And when we take into account other factorsand intuitions, these competitors to functionalism quickly lose their overallplausibility. For example, many contemporary philosophers would simplydiscount dualism as a serious candidate for explaining the ontologicalnature of mentality, primarily because of other difficulties that plaguedualism. So when we narrow the field to serious, viable hypotheses, like thetype-identity theory, then functionalism comes out on top.

In answer to this defense, two points need to be emphasized. First,remember that the phenomenon that needs explainingFthe explanan-dum of the ITBE argumentFis not the actual nature of the mind butrather our intuitions about the mind. The critical question is, Who has thebest account of our mental concepts? With regard to this question, thedualistic story and the cluster-concept story presented above are not at allimplausible. Whereas dualism may be improbable qua metaphysicalthesis, it is not so improbable qua psychological thesis about our folkconception. So when we properly see what the multiple realizabilityargument is actually about, it turns out that there really is a range ofserious alternatives to functionalism.

Second, as a matter of fact it is not at all obvious that the functionaliststory of mental concepts does a good job of accounting for otherintuitions we have. Indeed, a strong case can be made for thinking that,at least with regard to an important class of mental concepts, function-alism fares quite poorly. To illustrate this last point, I want to considerone further theory about our mental concepts that accommodates notonly multiple realizability intuitions but a host of other, counterfunction-alist intuitions as well.

Accounting for Our Qualia Concepts

Suppose that for a certain class of our mental concepts there really issomething like a defining essence, but that it concerns neither the mediumin which the mental states are instantiated nor the states’ relationalproperties. Instead, suppose it concerns the subjective, phenomenalaspect of the mental statesFtheir so-called what-it’s-like-ness. If thiswere so, then for the class of mental states picked out by such concepts,what would really matter for type identity would be what those states feltlike. Consider our ordinary concept of pain. Along with whateverrelational properties associated with our notion of pain, there are alsocertain subjective, experiential properties concerning how pain feels. Nowsuppose, as many have, that these experiential properties play the primaryrole in driving our categorization judgments. If we were presented withsome sort of hypothetical example and asked if the person or creature inquestion could be in pain, what would really matter to usFwhat would


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really drive our intuitive judgmentsFis what we thought the person orcreature was feeling at the time.

What is being suggested here is not anything terribly profoundor original. The proposal is simply that with regard to those stateswe normally characterize as ‘‘qualia,’’ our folk psychological concep-tion of those states individuates them not by virtue of their relationalproperties (as functionalists have claimed) but rather by virtue oftheir subjective, qualitative character. The idea that the subjective aspectof qualia is intuitively essential to their nature has hardly gone unno-ticed.9 What has been underappreciated, however, is how this hypothesis,when applied to our qualia concepts, can explain the same multiplerealizability intuitions that traditionally have been used to supportfunctionalism.

How might the supposition that our qualia concepts have a phenom-enal essence explain these intuitions? To account for these intuitions,all that is needed is the absence of an intuitive or conceptual link betweenthe physical medium in which the state is realized, on the one hand,and the subjective, qualitative character of the state, on the other. If thereis a large conceptual gap between these two, it would explain the intui-tive interchangeability of different realization bases. In other words, ifthe two sorts of properties are conceptually unrelated and intuitivelyindependent of one another, so that imagining the presence of one doesnot require imagining the presence of the other, then that would explainwhy we have the intuition that a neurological medium is unnecessaryand could be replaced without eliminating what’s essential to qualia.The question we need to address, then, is whether our conception ofthe phenomenal properties of qualia is sufficiently disconnected fromour conception of neurological properties to explain the multiple realiza-tion intuition.

For those familiar with the philosophy of mind, answering thisquestion is, if you’ll excuse the pun, something of a ‘‘no-brainer.’’ Arecurring theme since at least Descartes has been that we conceive of thesubjective aspect of the mental and the physical as radically different, andthat it is relatively easy to think of the one without the other. Indeed, ifthis weren’t the case, then various forms of dualism would be literallyinconceivable. On the other hand, the problem of other minds wouldn’tbe much of a problem if our ordinary conception of neurological statesintuitively required the presence of mental states. It is precisely the degreeto which the mentalFespecially the qualitative aspect of the mentalFisintuitively disconnected from the physical that makes the mind-bodyproblem so difficult.

9 As pointed out by an anonymous Metaphilosophy referee, both Perry 2001 and Loar1997 advocate accounts of our phenomenal concepts that focus on the experiential nature ofsuch states.



One philosopher who has emphasized this point is Saul Kripke. LikeDescartes, Kripke has argued against the identification of the mental withthe physical because of their conceptual independence. Briefly, Kripkeinsists that any form of mind-brain identity must be necessary, sincemental-state terms, such as ‘‘pain,’’ and neurological-state terms, like ‘‘c-fiber firing,’’ are both rigid designators. Yet it seems intuitively obviousthat the one could easily exist without the other. That is, there appear tobe possible worlds in which ‘‘pain’’ does not denote ‘‘c-fiber firing,’’ andvice versa. Hence, according to Kripke (1972), the relation betweenmental states and physical states cannot be one of identity.

There have been two related lines of response to Kripke’s argument,both of which are relevant for our discussion. The first stresses thatbecause Kripke’s argument only tells us something about the way wehappen to conceive of mental states, nothing follows about the actualmetaphysical relation that exists between the mental and the physical. AsJoseph Levine puts it,

[W]hat seems intuitively to be the case is, if anything, merely an epistemologicalmatter. Since epistemological possibility is not sufficient for metaphysicalpossibility, the fact that what is intuitively contingent turns out to bemetaphysically necessary should not bother us terribly. (1983, 350)

Levine’s point is similar to the one we discussed in section 2 concerningthe difficulty of establishing metaphysical claims about the mind on thebasis of what seems intuitively possible. For our purposes here, thecritical thing to note is that it is admitted by Levine and others that, atleast with regard to our conception of things, phenomenal properties aretreated as utterly distinct from neurological properties.

Now given this conceptual gap (which nearly everyone agrees is quitelarge), it would seem we have a perfectly straightforward explanation forthe intuition that pain could be realized in systems without neurons.Given that it is easy to imagine the existence of phenomenal propertieswithout the existence of any particular physical substrate, it seems thereis no need to appeal to functionalism to explain the intuitive multi-ple realizability of qualia. Our intuitive reactions to the Martian andprosthetic-brain cases are exactly what we should expect to find, givenwhat we know about the importance of phenomenal properties for qualiaand their conceptual disassociation from the physical. The intuitionthat functionalism has been invoked to explain already has a perfectlygood explanation: namely, the large disparity between our conceptionof phenomenal properties, on the one hand, and physical properties, onthe other.

This suggests that a second line of response to Kripke’s argu-ment should also be reconsidered. Some have argued that function-alism demonstrates that Kripke is mistaken in claiming that terms like‘‘pain’’ are rigid designators. If pain is type-identified with a certain


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causal role, then different things can instantiate pain in differentpossible worlds. Hence, functionalists claim that the mental and theneurological seem contingently related because they really are contin-gently related; the Kripkean intuition about the expendability of c-fibersis just a special case of the multiple realizability intuition explained byfunctionalism.

In rebuttal, Kripke has offered a fairly compelling reply to thisargument. He notes that the same intuitive contingency that existsbetween mental states and physical properties also appears to existbetween mental states and causal-functional roles (1972, 147). Hence,causal-functional roles appear to be every bit as contingent for qualia asneurological states. In the next section, I’ll provide some examples thatillustrate this point. For now, I want to offer a suggestion about howwe should view this debate. Given our preceding discussion, we can seethat the functionalist is correct in claiming that the Kripkean intuitionand the multiple realization intuition share a common explanation.The functionalist is wrong, however, in claiming that the proper explana-tion is that our qualia concepts treat casual-relational propertiesas essential. Instead, the two sets of intuitions are rooted in thespecial status our qualia concepts give to phenomenal properties. Whilethe standard functionalist response to Kripke’s challenge is to appealto the multiple instantiability that goes with functionalism to explainaway the Kripkean intuition, I’m now claiming that this gets thingsbackwards. We should instead explain the multiple realizability intuitionsas a by-product of what Kripke suggested all along; namely, that ourqualia concepts treat phenomenal propertiesFnot causal-relationalpropertiesFas essential.

Why should we think this account is the right one, that our qualiaconcepts employ phenonmenal features as essential and not casual orrelational features? To answer this question, I’d now like to turn to a hostof other well-known intuitions that support the phenomenal account andseriously undermine the functionalist picture. As we’ll see, a quick surveyof some other popular thought experiments shows that functionalismperforms rather poorly in handling other sorts of intuitive data.

Inverted Spectrums, Chinese Nations, and Zombies. If our mental conceptsreally are functional concepts, we should find that we judge systems thatare functionally similar to ourselves to be mentally similar. Yet in anumber of well-known thought experiments it is clear that our intuitivejudgments do not behave in this manner. For instance, it seems intuitivelypossible for there to be a creature whose ‘‘brain’’ is functionallyisomorphic to ours but who would nevertheless experience an invertedcolor spectrum (Shoemaker 1975). Alternatively, it seems possible forthere to be a complex system that is, again, functionally isomorphic to our



brainsFlike the nation of China simulating the neural activity of some-one in painFbut that doesn’t undergo any qualitative experiences (Block1980). Indeed, our conception of the mind is such that it seemsmetaphysically possible for there to be a person who is indistinguishablefrom a normal human in every casual or physical respect but who isnonetheless a mindless zombie (Chalmers 1996).

Cases like these pose a problem for commonsense functionalism be-cause the intuitions they generate are not what one would expect if ourmental concepts were truly functional concepts. Hence, the intuitionsserve as good reasons for rejecting the functionalist interpretation of ourqualia concepts. On the other hand, there is nothing surprising aboutthese intuitions if we assume that what really matters for our qualia con-cepts are the subjective, phenomenal features of qualia. If our conceptionof color experience is such that what really counts is the qualitative aspectof that experience, and if that aspect is conceptually removed from ourcausal-physical notions, then of course we are going to think it is possibleto have an inverted spectrum with someone who is functionally identicalto ourselves. If our notion of pain is such that the phenomenal dimensionof pain is far more important than anything else, and if that dimension isintuitively disconnected from our causal-physical notions, then, quitenaturally, we will judge it possible for there to be systems that are similarto ourselves in terms of their causal-physical architecture but that none-theless lack qualia. In short, what we have here is a set of intuitions thatcannot easily be squared with the functionalist account of our qualiaconcepts but are precisely what is to be expected on the phenomenal,qualitative account.

Mad Pain. Just as the functionalist account of our mental conceptspredicts that we should judge functionally similar systems as mentallysimilar, it also predicts that we should judge functionally dissimilarsystems as mentally dissimilar. However, in his well-known paper‘‘Mad Pain and Martian Pain,’’ David Lewis points out that it seemsintuitively possible for there to be an individual who possesses ordinarymental states even though the causal profile of those states is quite uniqueto the individual. For example, there could be a madman who feelspain when exercising on an empty stomach and for whom the state causesthoughts about mathematics. Lewis insists that if ‘‘I want a credibletheory of the mind, I need a theory that does not deny the possibilityof mad pain’’ (1980, 216). Yet this is exactly what does seem to bedenied on the functionalist account of our mental concepts. If thefunctionalist account of our mental concepts is true, and certain causalrelations are essential for our judgments about a mental state’s identity,then any dramatic change in a state’s causes and effects should underminethe intuition that the state in question is present. Consequently, the


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intuitive possibility of mad pain is a significant embarrassment forfunctionalism.10

On the other hand, the intuitive possibility of mad pain is exactly whatone should expect on the phenomenal analysis of our pain concept. Sinceintuitively the phenomenal aspect of our pain state is not dependent onthe state’s causal relations, those relations can vary without compromis-ing our intuition that pain is present. Mad pain is possible because, givenour conception of the mind, to be in pain is to be undergoing a certainstate that feels a certain way. How that feeling is caused, or what it causesin turn, is not essential for a positive categorization judgment. So here isanother intuition that is better explained by the phenomenal account ofour qualia concepts.

The Knowledge Argument. The essential features of functional conceptsare the represented causal or relational properties. Consequently, it isgenerally possible to achieve complete understanding of a functional kindby gaining knowledge about those causal-functional relations. When weknow everything a carburetor doesFhow it performs its function andinteracts with other components of an engineFwe have the sense that weknow pretty much all there is to know about a carburetor, quacarburetor. Notice that it would be very bizarre to have a functionalconcept in which, despite having learned of all the causal-functionalrelations involved, one still felt there was something essential missingfrom one’s understanding.

A number of writers, however, have suggested that in the case of qualiaexhaustive knowledge of the causal-relational properties associated with agiven state would intuitively leave something important out. One of thebetter-known arguments for this position has been provided by FrankJackson (1982). Jackson’s argument appeals to the possibility of a neuro-scientist, the now-famous Mary, who learns all of the causal-physicaldetails of color vision in a black-and-white environment. Intuitively, des-pite her exhaustive neurophysical knowledge, Mary would remain ignor-ant about certain essential facts concerning red experience. If she were to

10 It should be noted that Lewis himself denies that mad pain undermines functionalism.According to Lewis, our conception of the mind allows mad pain because the madman is inthe neural state that, in the majority of humans, plays the appropriate causal role of a personexperiencing pain. This similarity with others explains why we are inclined to classify themadman as a feeler of pain. This way of viewing things has serious problems, however. Forexample, it appears that the stipulation that the madman is neurologically similar toourselves (that is, in a specific neurological state that is shared by normal people) is not evenneeded to generate the intuition that he is in pain. It seems intuitively possibleFat least foreveryone I’ve talked toFfor someone to be in pain even though that person’s brain state isboth causally and neurologically unique. So long as we are told that the person’s state isphenomenologically similar to an ordinary person’s pain state, we are inclined to say theperson’s mindFthough quite oddFis undergoing a pain state.



see a red object for the first time, it seems obvious that she would learnsomething new about the nature of red experience.

Were our concept of red qualia actually a functional concept, we wouldexpect a certain intuitive response to Jackson’s thought experiment. Uponhearing of Mary’s complete knowledge of the various causal relationsinvolved in red visual experience, we should be inclined to attribute toMary full knowledge of the relevant state. But in fact we don’t. Instead,even for those who disagree with Jackson’s conclusions, it must beadmitted that there exists a strong intuition that Mary is ignorantFde-spite her causal knowledgeFabout the essential nature of red experience.This isn’t what we would expect to find if our qualia concepts werefunctional concepts. While the Jackson argument is intended to challengeall physicalist accounts of the mind, we can see that it undermines thefunctionalist interpretation of our mental concepts as well.

Going the other way, the intuitions that Jackson exploits are exactlywhat one would expect on the phenomenalist interpretation of our qualiaconcepts. If these concepts treat the subjective ‘‘what-it’s-like-ness’’ ofqualitative states as essential, and if it is impossible to know about thisaspect without having experienced the state in question, then the intuitiveresponse to the Mary case is exactly what we should expect to find. In this,and other similar cases, a phenomenalist interpretation of our mentalconcepts nicely explains the intuitions involved; the functionalist analysisdoes not.

Summary

It is important to be clear on what I am, and what I am not, trying to doin this section. I am not trying to reintroduce various metaphysicalarguments about how difficult it is for functionalists to account forqualia. I am not doing metaphysics at all (at least not directly). Instead, Iam making a metaphilosophical claim about the source of the intuitionsthat drive these arguments. I am proposing that a nonfunctionalistunderstanding of our qualia concepts does as good a job as a functionalistunderstanding with regard to explaining our multiple realizability intui-tions, and it also explains an array of other intuitive judgments that can’tbe explained by the functionalist interpretation. The phenomenalistaccount of our qualia concepts explains the multiple realizability intui-tions, the ‘‘functionally similar but mentally different’’ intuitions, the‘‘functionally different but mentally similar’’ intuitions, and our intui-tions regarding the incompleteness of causal-physical knowledge ofqualia. The functionalist account only explains the multiple realizabilityintuitions. That puts the score at four to one in favor of the phenomen-alist account, which strongly suggests it is the proper way to regard ourfolk-psychological concepts of qualitative mental states.


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Two other points are worth noting in connection with these moretraditional qualia-based objections to functionalism. The first is that theintuitions generated by thought experiments like Block’s Chinese nation,Lewis’s mad pain, and Jackson’s ignorant neuroscientist are generallyassumed to be unrelated and self-contained. As we’ve just seen, however,they are all exactly the intuitions we should have if our qualia conceptstreat phenomenal properties as essential. Hence, one added benefit of thisanalysis of our folk psychology is explanatory unity with regard to a widerange of intuitions. Seemingly divergent intuition-based complaintsagainst functionalism actually stem from a common conceptual source.

The second point is that up to now the defender of functionalism couldconcede that there are a few intuitions about qualia that prove embarras-sing for his or her theory, but nevertheless fall back upon the strength ofthe multiple realizability argument, which appeared invulnerable fromthese attacks. We can now see, however, that this is not the case. Thesecriticisms actually do harm the multiple realizability argument, as theylend credence to a nonfunctionalist interpretation of our mental conceptsand hence a nonfunctionalist explanation of our multiple realizabilityintuitions. It is a mistake to think the imagination-based multiplerealizability arguments are insulated from these other intuition-basedobjections.

4. Conclusion

The goal of this article has been to deflate the support that the conceptualversion of the multiple realizability argument provides for functionalism.Once we see how the argument is supposed to work, we can also see theways in which it doesn’t work. Since alternative explanations exist for ourjudgment that we can vary the physical stuff and retain the same mentalstates, and since those alternative explanations have a significant degreeof independent plausibility, we can no longer treat functionalist analysisof folk psychology as the only serious explanation for these intuitions.With respect to our conception of qualia, the functionalist account doeseven worse. Here, we already have a nonfunctionalist account of ourmental concepts that explains the intuition that the physical medium isirrelevant to the mind, and this account is superior to functionalism inaccommodating other important intuitions we have.

While other arguments for functionalism exist besides the conceptualversion of the multiple realizability argument, few have played asimportant a role in promoting its widespread popularity. Given theproblems discussed here, we can now see that this popularity is unwar-ranted. Without the support of the intuition-based multiple realizabilityargument, functionalism loses a great deal of its attractiveness, both as atheory of about our mental concepts and as an account of the mentalstates those concepts denote. Philosophers have failed to appreciate this



because they have ignored metaphilosophical questions about the sourceof multiple realizability intuitions. By focusing on these questions, we cansee how these intuitions ultimately fail to support what many take to bethe received view about the mind.11

Department of Philosophy203 Malloy HallUniversity of Notre DameNotre Dame, IN [email protected]

References

Armstrong, David. 1981. The Nature of the Mind. Brighton, Sussex:Harvester Press.

Batterman, R. 2000. ‘‘Multiple Realizability and Universalizability.’’British Journal of Philosophy of Science 51:15–45.

Bechtel, William, and Jennifer Mundale. 1999. ‘‘Multiple RealizabilityRevisted: Linking Cognitive and Neural States.’’ Philosophy of Science66:175–207.

Block, Ned. 1980a. ‘‘Troubles with Functionalism.’’ In Readings in thePhilosophy of Psychology, vol. 1, edited by N. Block, 268–305. Cam-bridge, Mass.: MIT Press.

FFF. 1980b. ‘‘Introduction: What Is Functionalism?’’ In Readings inthe Philosophy of Psychology, vol. 1, edited by N. Block, 171–84.Cambridge, Mass.: MIT Press.

Chalmers, David. 1996. The Conscious Mind: In Search of a FundamentalTheory. Oxford: Oxford University Press.

Clement, John. 1983. ‘‘A Conceptual Model Discussed by Galileo andUsed by Physics Students.’’ In Mental Models, edited by D. Gentnerand A. Stevens, 325–39. Hillsdale, N.J.: Lawrence Erlbaum.

Couch, Mark. 2004. ‘‘Discussion: A Defense of Bechtel and Mundale.’’Philosophy of Science 71:198–204.

DePaul, Michael, and William Ramsey. 1998. Rethinking Intuition: ThePsychology of Intuition and Its Role in Philosophical Inquiry. Lanham,Md.: Rowman and Littlefield.

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11 I am grateful to David Armstrong, Marian David, Carl Gillett, Eric Marcus, DeanZimmerman, and three anonymous Metaphilosophy referees for helpful comments andsuggestions. Earlier drafts of this article were presented at Illinois State University and theUniversity of Utah, where the audiences provided very helpful feedback.


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Kripke, Saul. 1972. Naming and Necessity. Cambridge, Mass.: HarvardUniversity Press.

Levine, Joseph. 1983. ‘‘Materialism and the Explanatory Gap.’’ PacificPhilosophical Quarterly 64:354–61.

Lewis, David. 1980. ‘‘Mad Pain and Martian Pain.’’ In Readings in thePhilosophy of Psychology, vol. 1, edited by N. Block, 216–22. Cam-bridge, Mass.: MIT Press.

Loar, Brian. 1997. ‘‘Phenomenal States.’’ In The Nature of Consciousness:Philosophical Debates, edited by N. Block, O. Flanagan, and G.Guzeldere, 597–616. Cambridge, Mass.: MIT Press/Bradford Press.

Maudlin, Timothy. 1989. ‘‘Computation and Consciousness.’’ Journal ofPhilosophy 86:407–32.

McCloskey, Michael. 1983. ‘‘Naive Theories of Motion.’’ In MentalModels, edited by D. Gentner and A. Stevens, 299–324. Hillsdale,N.J.: Lawrence Erlbaum.

Perry, John. 2001. Knowledge, Possibility and Consciousness. Cambridge,Mass.: MIT Press.

Polger, Thomas. 2004. Natural Minds. Cambridge, Mass: MIT Press/Bradford Press.

Putnam, Hilary. 1975. ‘‘The Nature of Mental States.’’ In Mind, Lan-guage and Reality, volume 2 of Philosophical Papers, 429–40. Cam-bridge: Cambridge University Press.

FFF. 1988. Representation and Reality. Cambridge, Mass.: MIT Press/Bradford Press.

Rosch, Eleanor. 1973. ‘‘Natural Categories.’’ Cognitive Psychology4:328–50.

FFF. 1978. ‘‘Principles of Categorization.’’ In Cognition and Categor-ization, edited by Eleanor Rosch and Barbara Lloyd, 27–48. Hillsdale,N.J.: Lawrence Erlbaum.

Shapiro, Lawrence. 2004. The Mind Incarnate. Cambridge, Mass.: MITPress/Bradford Press.

Shoemaker, Sidney. 1975. ‘‘Functionalism and Qualia.’’ PhilosophicalStudies 27:291–315.

Wellman, Henry. 1990. The Child’s Theory of Mind. Cambridge, Mass.:MIT Press/Bradford Press.



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