Causal Theories of Mental Content

Theories

Nomic Covariation

Advantages of Covariation Theories

Covariation Theories and the Disjunction Problem

Functional Role Semantics

Advantages of Functional Role Semantics

Problems for Functional Role Semantics

Causal Theories and Cognitive Science

Bibliography

Other Internet Resources

Related Articles

Introduction 

Very few people deny the  platitude that minds causally interact with the world.  Causal theories of mental content suppose that such causal connections not only facilitate the mind's interactions with the world, they provide the basis of mentality.  A large part of understanding the nature of the mind is understanding how it comes to be aware of the world.  Theories of mental representation develop in the context of some or other representational theory of mind (RTM).  A representational theory of mind holds that mental states have intentionality (are about the world) in virtue of a representational relationship holding between the mental state and the object.  Most philosophical theories of mental content hold that mental states represent the world in virtue of the sorts of causal relationships those states have within the mind and/or with the world.  Historically, monistic physicalists find causal theories attractive; philosophers interested in understanding all mental properties, states, and/or events (and all of existence)  in terms of physical properties, states, and/or events.  Such naturalistic philosophers seek to understand the mind as purely physical in origin and nature.  The main body of this article discusses the historical precedents of contemporary causal theories of mental content as well as the two major categories of causal theories of mental content current in the philosophical literature.  In each case the article outlines the theory, discusses its advantages and strengths, raises commonly perceived problems for the theory, and presents responses by proponents of the theory.  

Historical Precedents

Though many theories of mental content are causal theories, not all theories of mental representation are causal in nature.  For example, Locke supposes that ideas of primary qualities represented qualities in an object, not through reliable causation, but because they were similar (share the same properties). Contemporary theories of mental content have predecessors dating back to Book III of John Locke’s Essay Concerning Human Understanding, possibly Aristotle’s De Anima , or even to Plato’s Theatetus.  Locke’s notion of secondary qualities (a quality or power of the object to cause particular ideas in us which bear no similarity to the object, e.x. color) looks very much like a contemporary causal theory based upon reliable causally mediated covariation  (Cummins 1989).  Aristotle’s discussion in Book II of De Anima suggests that, for example, color in the object is different from our sensations of color, which are nevertheless reliably caused by light hitting the object.  Similarly, Plato’s analogy of perception as the matching of sensations caused by the world to the impressions (knowledge) upon a ball of wax also suggests that Plato entertained the notion that the sharing of essential natures between mental representations and objects in the world allows one to represent those objects as instances of kinds.   Contemporary causal theories of  mental representation have developed in the theoretical context of explanation in cognitive science.  It can be helpful to view the intended role of such causal theories in computational explanations in cognitive science.  However, contemporary causal theories can be understood independently of their role in cognitive science.  Sidebar on Explanations in Cognitive Science
 

Theories
There are two general causal theoretical approaches to a theory of representation in the contemporary literature.  Neither theoretical approach regarding the representation relation has gained general acceptance.   However, there are several agreed-upon constraints for a theory of representation.  First, the representation relation must be consistent with the physicalistic nature of cognitive science and science generally.  Second, the relation must be present and explanatory in accepted explanations within cognitive science. (an appropriate characterization of "accepted" explanations is somewhat controversial).  Philosophers particularly would also like to see the accepted theory of representation explain many of the widely accepted properties of belief.  Block (1986) and Fodor (1988) provide discussions of the potential problems, the solutions to which many philosophers hope to find in a theory of mental representation. 
 

One theoretic approach to articulating the representation relation, "Nomic (law-like) covariation" or "covariation," postulates a simple causal relationship between the object or property and the state that represents the object or property.  The other approach, "functional role semantics," hypothesizes that a state has content in virtue of the state’s occupying a particular position in a complex web of causal relationships characterizing the cognizer’s functioning.  Candidate content-fixing causal relationships include causal relationships within the cognizer (i.e., relations between brain states) and/or without (i.e., relations to the distal environment).  Both functional role semantics and covariation theories satisfy the (above) first, physicalistic constraint by hypothesizing that a cognizer’s states represent the distal environment solely as a result of the specific sorts of causal connections had by those states.  The theories diverge in terms of the specific causal relationships each emphasizes.

Covariation
Covariation theories hypothesize that a state represents an object or property in virtue of a causal connection between the object or property in the world and the state that represents that object or property within the cognizer.   Information theory as well as work within a psychophysics inspire contemporary covariance theorists.  Fodor, for instance, notes that: 
 

Covariation theories, as a result, seem to satisfy the second constraint upon theories of representation, i.e., that the relation must be present and explanatory in accepted explanations within cognitive science.  For example, Hubel and Wiesel (1977) investigate the representational content of cells in the striate (visual) cortex by monitoring the activity of those cells looking for preferential relationships between the activity of these cells and the presence of properties in the visual field.   A system’s states represent those objects and/or properties of the distal world with which they covary according to covariation theories.  Specifically, covariation theories assign contents to states via some version of the following definitions:
   

    Illustrative animation

Advantages of Covariation Theories
Intuitive Appeal
The intuitive appeal of covariation theories stems from the idea that a cognizer represents an object or property by being causally "in tune" with that object or property.  The causal connection provides a concrete connection between the object/property and the state which represents it.  It also insures that the state represents elements of the cognizer's distal environment.  

Punctate Content

Covariationists such as Jerry Fodor advocate the approach because covariation assigns content to individual states independent of how the cognizer operates upon those states (inferences it can make) and/or the content of other states with which the state might interact.  Fodor refers to this assignment of content as "Punctate Content," or "atomic content."  Among the advantages claimed by Fodor for punctate content is that it allows for content identity across individuals who have quite different theories regarding some object or property.  Similarly, punctate content provides the only theory whereby people can refer to real objects even when they have great numbers of false beliefs about them.  For instance, Fodor claims (1992) that Aristotle thought about and talked about the same things we refer to by "stars" even though he falsely believed stars to be relatively close and rotating around the Earth on glassy spheres.

Systematicity and Compositionality

Whereas the punctate content argument for covariation theories supposes that fixing the content of representational states in isolation from inferences in which the state might participate lends nomic covariation an explanatory advantage with regard to content identity, the systematicity and compositionality argument supposes that covariation theories better explain perceived truths about the combinatorial properties of language and concepts.  Compositionality is the theory that the meaning of a complex expression in a language results from the meanings of its constitutive elements and their relationship within the complex expression.   Compositionality plays a central role in many linguistic theories, since its supposition for both language and thought provides a fairly straightforward explanation of the human ability to grasp an enormous number of different thoughts of varying complexity and their corresponding linguistic expressions.  For instance, because we understand the individual elements like "cup" and "coffee", we understand the complex expressions "cup of coffee," "hot coffee," "coffee gives me the shakes," etc..  One explains our understanding by noting that the meaning of these complex sentences is built-up from the meaning of their constitutive elements and their combination within the complex sentence.  Furthermore, languages and thoughts seem to have a systematic structure to their compositionality.  For example, one seemingly cannot have the thought that "coffee has more kick that tea" without also being capable of thinking that "tea has more kick than coffee."   Proponents of covariation theories (Fodor and Pylyshyn 1988, Fodor and McLaughlin 1991) argue that such seeming facts about thought and language are naturally explained by covariationist semantics.  See Cummins et al (2001) for a forceful rebuttal.

Epistemology and Representation

A final perceived advantage for covariation approaches lies in that they provide a clear-cut mechanism through which a cognizer can come to know about an object or property in the world in virtue of their representational capacities.  A cognizer that represents an object or property in the environment does so insofar as the cognizer can reliably detect the object’s presence.  (Dretske, 1989)
 

Covariation Theories and the Disjunction Problem
The most widely discussed problem for covariation theories is called the "Disjunction Problem."  According to covariationists, a state represents an object or property when the system tokens (enters into) that state when confronted with the object or property and only when confronted with that property. However, suppose that cognizer tokens a state, S _c, in all of its cat interactions. According to the when clause of the covariationsist definition, the cognizer’s state appears to represent cathood. Unfortunately, one night the cognizer tokens an S _c when seeing a skunk in the darkness. The only when clause of the definition prima facie dictates that S_c never really represented cathood simpliciter.  Rather, the cognizer has always represented a property that we can only describe using the disjunction, "cat or skunk."
 
Illustrative Animation
 

The disjunction problem poses two related difficulties for covariation theories: First, the theory seems to dictate counterintuitive representational contents for states. If one has beliefs about cats, (e.x. cats are domesticated felines that have a number of distinct breeds), then covariation seems to dictate that those beliefs have always been about things having the property  cat or  skunk.  Second, the disjunction problem seems to demonstrate that covariation cannot account for misrepresentation, since any seeming case of misrepresentation by a cognizer becomes a correct representation of a disjunctive property under covariation.  In other words, one never mistakenly believes that one sees one's mother at the corner, one always correctly believes that "mother/other" is at the corner.

The Two-Case Strategy
Theorists have explored a number of solutions to the disjunction problem.  However, all of these solutions rely upon some form of the idealization strategy: A given solution will separate cases of the tokening (occurrence) of a state into two groups, one class in which content is already fixed and representational error can occur (normal conditions), and a second class (ideal circumstances) in which content is fixed by perfect covariation. There are several important versions of this solution.

Ideal Conditions
To solve the disjunction problem, one must modify the basic covariation theory so that the cognizer represents "cat" and not "cat/skunk" despite occasionally mistaking skunks for cats.  Advocates of the ideal conditions solution to the disjunction problem hold that under ideal perceptual conditions (i.e., in good light, at close distance, etc.) one can distinguish cats from skunks. Thus, they suggest cognizers represent cats as cats because of their discriminatory capacities under ideal circumstances.  Idealization in mainstream science is both the inspiration behind the covariationist’s idealization strategy and its source of tacit plausibility.  In normal cases of scientific idealization theorists ignore certain negligible parameters in real systems to formulate a law. The resulting law, though not strictly true of any actual system, proves predicatively adequate, and quantifies a real relation in actual physical systems.  For example, real gases are not composed of Newtonian molecules in that they are not point masses, nor are their collisions perfectly elastic. Likewise, heat is not the only energy source present in gases. In most cases, however, other parameters (like electromagnetic forces) prove negligible.  One idealizes away from such negligible parameters to quantify the inverse relationship between, on the one side, the pressure and volume of a gas, and on the other side, the temperature and number of moles.  Idealizing away from other parameters results in the ideal gas law: PV = nRT.

The move toward idealization in response to the disjunction problem attempts to emulate noncontroversial cases of scientific idealization like the above-described ideal gas law. The basic idealization move defines representation as follows:
 

On the idealization line, S_c represents cats as cats since, under ideal circumstances, the cognizer tokens S_c s when, only when, and because of the presence of instances of cathood.  State S_c does not represent "cat or skunk" because under ideal circumstances skunks do not cause the cognizer to token S_c.  Such an idealization from error, admits the covariationist, breaks down in abnormal circumstances.  Nevertheless, the idealization allows psychological laws to capture a real relation (the representation relation) in actual systems.  Moreover, since most cases are close to ideal circumstances, psychological laws utilizing idealized covariation prove predicatively adequate.

The covariationist’s ideal conditions solution divides tokenings of a state by a system into content-imbuing (ideal) and content-fixed (malfunctioning/atypical) classes.  Covariationists assert that one legitimately idealizes away from error because errors since errors prove coextensive with the cases of malfunction and/or atypical situations from which one legitimately idealizes.  For example, if one pulls a weighted spring hard enough to bend or break the spring, it will no longer obey the standard harmonic oscillation equation.  Such spring systems do not undermine the the basic physics of dampened harmonic oscillatory systems because the circumstances are such that the spring system cannot operate qua spring system.  The same holds for cognitive malfunctions: One’s tokening of an S_c as a result of an amphetamine induced psychosis does not introduce disjunctive content because amphetamine induced psychosis is a case of mental malfunction.
 

Of course, all skunk-caused instances of S_c will not trace their origins to malfunction.  One could token a S_c as a result of the same cat-like features prompting tokenings of S _c for cats.  Dismissing such look-alike cases as malfunctioning requires one also dismiss cat cases as malfunctions.  All cognition becomes malfunction, if one focuses exclusively upon malfunction in specifying ideal conditions.  Consider another example.
 

Illustrative Animation
 

Subjects normally judge the right side of the above figure to have a much darker shade of purple than the left side.  In fact, the surface reflectance of the purple areas of the figure remains uniform (it is all the same color of purple).  Psychologists refer to the mistaken judgment as "the assimilation effect".  Psychologists explain the assimilation effect by attributing the mistake to the pooling together of signals from several retinal cells.  In most circumstances, pooling reduces equivocation (error or noise) arising from false signals by individual retinal cells. However, when one closely intersperses the dark and light patterns throughout a visual field, pooling serves to inhibit or to excite cell firing, resulting in a misrepresentation of relative shading.  So, a case of normal functioning--in fact, functioning that acts to reduce error--results in misrepresentation.
 

Covariance theorists respond to such normal functioning cases by appealing to atypical conditions.  For instance, when the pressure upon a gas exceeds atmospheric level (1.013 x 105 N/m2), or when its temperature becomes too great, the negligible parameters ignored by the idealized gas law become non-negligible.  The predictive accuracy of the idealized gas law plummets, though the gas does not malfunction.  Nevertheless, these cases do not count against the idealized gas law because the circumstances are atypical.  The covariationist likewise claims that circumstances are perceptually atypical, that is, less than ideal, when the system tokens a S_c in response to a cat.
 

The covariationists’ move looks suspiciously circular unless they can specify an independent means of ruling out case of similar features as atypical.  In other words, one must define ideal conditions so that malfunction and atypical circumstances prove coextensive with error.  But one cannot avail oneself of the notion of error, nor of other intentional or semantic notions in formulating and motivating the definition.  One must have a reason for labeling the skunk to S_c cases as less than ideal, and the reason cannot be that skunks cause cat tokens (S_c) in feature similarity cases.  For example, in the movie "The Crying Game" an Irishman trying to escape from the IRA becomes romantically involved with a woman.  However, much to the surprise of the Irish man (and the audience) this woman is actually a man.  The reaction of the  Irishman clearly shows he misrepresented the gender of his romantic partner.  Yet, the Irishman did see his partner in good light, at close distance, etc..  The natural solution to this difficulty attempts to take advantage of the idea that there are conditions under which such a sex difference would not escape notice.  However, in specifying such conditions as ideal conditions for this case, one must be guided in a circular manner by one’s knowledge of the property that the state actually represents.
 

Additionally, critics (Wallis 1994 and 1994a) argue that appealing to idealization to defeat the disjunction problem is strongly and negatively disanalogous with successful uses of idealization is science.  For example, in order to explain misrepresentation in cases of malfunction or atypical circumstances, the covariationist must rely upon the content dictated by idealized  covariation.   When a skunk causes an S_c because bad lighting, the covariationist must suppose that S_c represents cats in order to explain why the person misrepresented the skunk as a cat.  Thus, for the covariationist the results of the idealization are applicable in conditions which violate the presuppositions of the idealization.  In contrast, when the pressure upon a gas exceeds atmospheric level (1.013 x 105 N/m²), or when its temperature becomes too great, the negligible parameters ignored by the idealized gas law become non-negligible.  In these atypical circumstances physicists will agree that the ideal gas law does not apply since the presuppositions of the idealization do not hold.  Thus, while the mainstream use of idealization is limited to ideal or close to ideal circumstances, the covariationist  cannot accept such limitations.
 

Learning Periods
Fred Dretske (1981, 1989) suggests that content gets fixed for a state during a learning period.  In this period, a cognizer develops a perfect causal connection between the state and the object or property with the help of an instructor who provides examples and corrections.  Once the learning period ends, the cognizer’s state has a fixed content and tokenings of the state in cases where the object or property is not present count as misrepresentations.
 

Or, to adopt probabilistic formulation more consistent with Dretske's work:
 

Fodor (1988) and others have criticized this approach on two grounds.  First, Fodor argues against the existence of a principled distinction between learning and non-learning periods.  Hence, if Dretske cannot offer a principled ground for distinguishing between learning and non-learning periods, then Dretske has no basis upon which to call some tokenings of the state content imbuing and others representing or misrepresenting.  Second, even if one could rigorously specify a learning period, learning during this period seems to provide no principled distinction between the univocal and disjunctive causal connections.  Critics ask, "if one tokens S_c for both cat and skunk in the post-learning period, why should suppose that the causal connection created in the learning period actually holds between cats and S_c and not between cat/skunk and S_c ?"  Worse still, why isn't the content "learning period cat or post-learning period cat/skunk"?

Philosophers also offer the following standard criticisms of the learning periods approach.  First,  a cognizer can prima facie only represent those objects/properties for which it has had a learning situation.  Thus, on the learning approach there can be no innate knowledge.  Second, cognizers do not seem to learn to identify properties and objects with perfect reliability as required by Dretske.  Finally, since learning is a historical fact about a cognizer and a duplicate does not share one's learning history,  the states of one's molecule for molecule duplicate would seem to lack the content had by one's own states.  (Such examples duplicate examples appear in Burge, 1979, Cummins 1989, Davidson 1987, and Putnam 1975).

Teleological Accounts
Advocates of a teleological solution to the disjunction problem, such as  Dretske (1988), Millikan (1983 and 1986),  Neander (1995 and 1996), Papineau (1984), Shapiro (1992 and 1996), and Sterelny (1990) suggest that evolutionary history (evolution or learning for Dretske) determines content.  For example, a frog captures and eats any ambient moving dot in its visual field.  As a result, hungry frogs eat ball-bearings rolled in front of them.  Advocates of the teleological account claim that frogs misrepresent ball-bearings as flies because the function of a frog’s visual cells is determined by the uses of those cells responsible for a frog’s ability to propagate its genome, i.e., uses involving fly capturing.  Such an account would define representation as follows:
 

There is one caveat to the above definition in that the notion of representation for teleosemanticists might be more like representing the presence of C at a time. |

Two major distinctions appear among teleological theorists.: (1) whether the content-determining functions are those of  belief-generating mechanisms generically or of individual beliefs specifically and (2) whether one should assess the function of states relative to producers of those states, or to the consumers of the states.  For example, Millikan holds that adaptational history determines the function (and hence, the content) of specific beliefs.  The content of the frog's visual state "fly," has an indicative function and content of fly, in virtue of the state's past co-occurrence with flies.  Others (ex. Papineau) hold that selection determines the function of belief-making mechanisms.  Thus, the state means fly because the mechanism, the frog's visual system, that produced the state has the selective function of indicating the presence of objects in the distal environment.  Some teleologists  (ex. Millikan), likewise emphasize that the function of the state for consumers of the state determines content.  Others suppose that the function of the producers of the state determines the state's content.  Thus, for Papineau the function of the visual system (the producer of the state) determines its content,  In contrast, the fact that S_c triggers the frog's capturing mechanism (the consumer)  gives S_c its indicative function on Millikan's account.     

Fodor (1988) criticizes teleological accounts on the ground that evolution does not select with sufficient precision to account for typical univocal content claims.  If a frog represents ambient dots as "fly or ball-bearing" in a fly-rich, ball-bearing-poor environment, then that disjunctive representational content would account for the frog’s ability to propagate its genome.  Hence, claims Fodor, evolutionary history will not favor "fly" over "fly-or-ball-bearing" as the content of frog visual cells.

Two other objections to teleological accounts appear in the literature.  First, most artifacts (e.x., compact discs, SUVs, etc.) in the human environment were not present during a significant portion of human evolutionary history.  As a result, advocates of teleological solutions to the disjunction problem must explain a huge percentage of the representational capacities of humans, including the representations of many ordinary objects like chairs or beer, by definition.  Second, because teleological accounts appeal to the evolutionary history of a cognizer to explain representational abilities, any seeming representational abilities without such a history would not have representational content on the teleological account   For example, if a molecule for molecule duplicate of Millikan where to spontaneously appear, it would seem to have all of her cognitive/representational abilities.  Yet, on Millikan’s account, her exact double would not have any states with representational content.  (Cummins, 1989, Davidson, 1987).

Asymmetric Dependence
Fodor’s (1990) asymmetric dependence theory suggests another twist on the general idealization strategy.  In addition to a nomic connection between a state, S_c, and an object/property (cathood) asymmetric dependence theories define representation in terms of two counterfactual scenarios: 
 

Illustrative Animation
 

As above, asymmetric dependence rules out potentially troublesome cases because of the existence of a counterfactual set of conditions in which subjects can distinguish cats from skunks.   Critics (Cummins, 1989, 1997, and Wallis 1995) argue that asymmetric dependence theories fare no better than other versions of nomic covariation.  One difficulty is that the brain recognizes higher level concepts through the detection of features.  As a consequence, it appears that there is no asymmetric dependence between cases, or worse, it goes the wrong way from fake to representation.   For instance, if I find my car by looking for features x,y,z, then I can break the car to S_car connection by altering the appearance of my car.  But that will not break the look-alike car to S_car connection (violating 2).  If, on the other hand, I break the look-alike car to S_car connection (say by altering my beliefs about my car’s appearance), then it seems I do break the car to S_car connection (violating 1).  One can tell similar stories in terms of the normal, albeit somewhat noisy, functioning of cells in the visual system. (Wallis 1995).
 

Other philosophers have forwarded other objections.  Adams and Aizawa (1997) argue that Fodor's conditions commit him to the retinal projections of properties and objects instead of the properties and objects themselves.   Antony and Levine (1991) as well Wallis (1995) argue that Fodor's theory runs counter to other aspects of his own account of mentality.  
 

Other Problems for Nomic Covariation
Semantic Reduction and Verificationism
In addition to the disjunction problem, another objection challenges to the ability of covariation theories to explain the representational capacities of states with regard to objects/properties beyond low-level perceptual properties (e.x. color).  One can make one's best case for law-like covariation determining the content of states representing low-level properties like red or zero-crossing.  One might even extend the notion to ordinary, medium sized objects/properties like table or cow.  However, at some point, probably early on one must suppose that states represent properties and objects of a higher levels of abstraction, at least one's like electron, in virtue of their being defined (perhaps even implicitly) in terms of the representational properties of lower level states.
 

Robert Cummins (1989, 1997) objects to this strategy, claiming that the covariation of mental states with objects/properties requires that the cognizer represent heuristic information either implicitly or explicitly.  Thus, covariation will not explain the representational properties of any states but the most primitive representational states.  All higher level concepts from dog to democracy must get meaning through definition.  At first glance, it seems plausible to suppose that states that represent high-level theoretical properties like electron get their meaning through definition in terms of lower level properties. After all, such properties and objects often have theoretical definitions. However, the failure of such semantic reductions has shaped the history of western philosophy and mathematics (Quine 1951). The logical positivists, for instance, held that the meaning of terms was just the conditions for their verification (the verificationalist theory of meaning).  However, no generally accepted means of spelling out such conditions emerged.  Covariation’s critics ask, "if the state one uses to represent crow gets its meaning from being defined in terms of lower level properties, then why does one have difficulty in articulating that definition in any but the most superficial sense?" Psychological research also appears to run contrary to semantic reductionism in that it indicates that object recognition and categorization are strongly influenced by perceptual features, the exact make-up of which is somewhat variable and fluid.
 

According to Cummins, mental states achieve covariation with cats because we already have explicitly represented or implicit knowledge about cats (ex. they are domesticated felines). Further, if covariation is not the simple, unmediated causal relationship between the property/object and the state, but rather the result of often complex causal interactions within the system, then this suggests that covariation is really just another instance of its competitor, functional role semantics.  Similarly, Wallis argues that visual object recognition is itself a cognitive task and as such appeals to rather than explains mental representation. 
 

Failure of Univocal Feature Detection for Low-Level Properties     

Finally, some theorists like Kathleen Akins (1996) (also Churchland and Sejnowski 1992 and Wallis 1995) argue that the various cells that perform sensory transduction are not properly characterized as the sorts of feature detectors required by nomic covariation.  Such sensory cells do not respond exclusively to the presence of some particular object or property, but can and do respond to other properties.  Their responses are not all or nothing.  Rather, they show "selective sensitivity" to properties in that they respond to a wider range of stimulus, but respond more strongly to certain stimuli.  For example, rods and cones in the retina are often portrayed as representing a certain wavelength of light.  The response curves of these cells in fact overlap dramatically.

Thus, the same response can be elicited from a red cone by similar levels of blue or green light.  Additionally, perception is riddled by often useful confabulations by the sensory systems.  For example, rod and cone activation is represented by averages of pooled cells almost immediately in the visual system.  This has a good effect in that it eliminates noise from sources like body heat, but can also lead to the assimilation effect noted earlier.  Similarly, the visual system compensates for the blind spots in each retina were the cells leave the eye by "filling in" that area.

blind spot

The Problem of Depth

Covariationist intend their definition to capture a representation relation between states of the cognizer and objects and properties in the immediate distal environment.  However, causal covariation occurs at a number of stages in the causal chain leading to the tokening of a state by a cognizer.  At one extreme, all states of a cognizer happen when only when and because of the big bang.  At the other extreme, S_c will covary with some set of patterns of retinal stimulation.  Covariationists must find a way to rule out all links in the causal chain except the object/property in the immediate distal environment.  For example, retinal stimulation patterns might be ruled out as candidates for content because of the multiplicity of patterns that cause a single state.

Illustrative Animmation

Non-existent Objects

Explaining the content of states that intuitively represent non-existent objects or properties poses yet another challenge for covariation theorists.  If people have states that represent the property of being a unicorn, it would seem that those states must covary with unicorns.  Since there are no unicorns with which a candidate state can covary, covariation theories do not seem to have a natural way to account for such representational abilities.  Fodor (1990) claimsthat his asymmetric dependence theory can handle such cases.  Another possible strategy for the covariationist would be to define non-existing objects.

Absent Qualia

Some philosophers, for example, Searle (1980), Maudlin (1989), and BonJour (1991) have also argued against covariation theories (in fact, against all causal theories) on the grounds that these theories are satisfied in cases where from the internal perspective of an agent, the agent lacks the necessary conscious awareness of content.  For these philosophers mental states that have intentionality (are about something) have a qualitative aspect to them.   
 

Searle (1980), for instance, argues that one can manipulate Chinese symbols having the appropriate causal connections to objects or properties in the world without thereby coming to understand Chinese.

Functional Role Semantics

Whereas covariationists focus upon a single causal connection in fixing content, advocates of functional role semantics (Block 1986 and 1987, Field 1977 and 1978, Harman 1987), suggest that the overall network of causal relations into which a state can enter fixes its content.  Often causal roles are specified functionally/computationally.  Versions of functional role semantics include "Conceptual Role Semantics," "Procedural Semantics," or "Inferential Role Semantics".  There are two versions of this approach, designated "wide" or "long-armed" and "narrow" or "short-armed".  Narrow functional role theorists limit the causal relations that determine content to those occurring between mental states.  Wide theorists allow connections to the distal environment and even social contexts to delimit the content of a state.
 

Illustrative Animation

Advantages of Functional Role Semantics

Unified Account of Content

Functional role theories have several attractive features.  For instance, functional role theorists do not need bifurcated accounts of representational content.  Recall that the law-like connection between state and property required by covariation theories seemed the most plausible for low-level properties like color or shape.  Therefore, covariationists had a difficulties accounting for a state's ability to represent higher-level properties and uninstantiated properties.  Thus, theorists often offer alternative accounts of the representation of these properties (like definition through low-level properties).  Functional role semanticists hypothesize that all states get their content in the same manner, via their functional role.  Hence, functional role theorists avoid difficulties in explaining the representation of high-level and uninstantiated properties.  They need not depend upon bifurcated accounts of representational properties.

Belief Change

Second, functional role theorists can easily accommodate the observation that changes in beliefs can result in changes in representational content, since changing beliefs will often change the functional roles of states.  For example, prior to the discovery of Multiple Sclerosis theorists thought that Polio was the only disease associated with fever, headache, stiff neck and back, muscle pain and tenderness, and, if there is involvement of the central nervous system, paralysis of essential muscles, such as those controlling swallowing, heartbeat, and respiration.  As a result, researchers were baffled by the seeming vaccine resistant cases of Polio.  The discovery of MS seemed to change the representational content of the mental representation of Polio.

Rationality Constraints on Belief Ascriptions

Finally, functional role theorists can capture the intuition that in trying to understand the representational content of another cognizer’s state, one is constrained by the heuristic that the overall set of content ascriptions must "make sense," i.e., be consistent with the supposition that overall, the cognizer’s interactions with the world are intelligent or rational.  For example, if someone saw an actual UFO the covariationist might well suppose that UFO was the content of their representational state.  However, if the person was the head of the UFO-Sceptics association and had a theory debunking the UFO interpretation of their experience.  The functional role theorist would likely not attribute the content "UFO" to the person's state.

Problems for Functional Role Theories
Semantic Holism
Theorists typically raise three distinct but related objections to all versions of functional role semantics.   First, to identify particular states in disparate individuals as states having the same representational content, functional role semantics prima facie requires that the states have identical functional roles.  Fodor (1992, 1987) among others has termed this view Holism,  about content (also Semantic Holism).  For example, suppose that it appears that both Bill and Bob believe that "Wallis’ article is enlightening."  That is, they both point to the same article, proclaim that it is enlightening, assign it in their class, etc..  However, the causal roles of their respective states differ in a single respect; Bill believes "Wallis is a pompous know-it-all," while Bob believes "Wallis is a precocious windbag."  Prima facie, functional role semantics dictates that Bill’s belief that "Wallis’ article is enlightening," has a different content than Bob’s.  Similarly, people with disparate cognitive or perceptual abilities seem to have disparate representational contents.  Thus, the theory appears to imply that the average human has a different concept of traffic light than color blind humans.
 

Functional role semanticists generally adopt one of two responses to the above objection.  One response strategy--by far the predominant strategy--merely takes a page from the covariation playbook and adopts a functional role version of the two classes strategy.  The  functional role version of the two classes strategy would prune the number and/or kind of causal or computational connections necessary for belief/content identity, thereby allowing for belief/content identity across individuals with somewhat different causal/computational roles.  In the above case, differences in beliefs that are peripheral to the belief that "Wallis’ article is enlightening" would not necessarily constitute the basis for content non-identity.

While the just-rehearsed response has intuitive appeal, critics (Fodor 1988) point to the potential difficulties in distinguishing core (central) beliefs or other causal links from peripheral ones in a manner that is not hopelessly unsystematic and ad hoc.  For instance, what causal connections (beliefs, desires, dispositions to take action, etc..) constitute the core of one’s belief that the colorless, tasteless, odorless liquid before one is water.  Need one know, to take a case, of the existence of deuterium oxide (heavy water), make appropriate inferences with regard to D₂O, discriminate between D₂O and H₂O, etc..  One might opt to the common strategy of including only analytic beliefs and corresponding inferences in the set of core beliefs and inferences in distinguishing core from peripheral beliefs and inferences.  Analytic truths are conceptual truths, those things true solely in virtue of the nature of the concept.  Such a suggestion requires a real distinction between analytic beliefs and non-analytic (synthetic) beliefs.  Many philosophers feel that Quine (1953/1970) has effectively undermined the robustness of such a distinction.  Similarly, Stich (1983) argues that judgments of belief/content identity are not as intuitively precise as advocates of the analytic distinction would seem to predict.
 

The second response to the prima facie difficulty of intuitively identical content across differing functional roles claims that while such beliefs are in fact non-content-identical, they are strongly content-similar.  The key concept here is the notion that belief identity is not a binary notion, but ranges from completely non-identical to completely identical (Cummins 1989).  The strength (or weakness) of this response lies in its ability to accommodate the intuition that Bill’s and Bob’s beliefs have the same content while simultaneously acknowledging the theoretical constraint that differences in functional roles dictate differences in content.


 

Critics of Functional role semantics (ex. Fodor, 1988) argue that a graded notion of content identity, in addition to being counterintuitive, undermines the ability to formulate psychological generalizations and subsume particular cases under those generalizations.  Cognitive science, they claim, would be reduced to the unworkable notion that Bill’s and Bob’s beliefs are, say, 97% content similar to the belief that Wallis’ article is enlightening and hence can be, say, 97% subsumed under generalizations regarding the belief that Wallis’ article is enlightening.  Furthermore, Fodor (1992 and 2001) claims colloquial notions of belief similarity like, "His notion of mental representation is similar to mine," as well as their theoretical counterparts presuppose a notion of belief identity that he claims cannot be provided by holistic theories in any cases where beliefs diverge.
 

Content Fixing, Error, and Univocal Contents
A closely related objection to that of holism is the argument that functional role theories have no non-arbitrary way either of fixing content. Specifically, functional role semanticists either cannot distinguish representational error from veridical representation, their theory results in non-univocal content ascriptions, and/or the theory results in multiple content ascriptions applying simultaneously to a given state.  For example, suppose that there are two worlds: one, call it Earth₁  in which there is no water, but in which D₂O (or some chemically different, but phenomenally similar substance) is plentiful; the other, call it Earth₂, where H₂O is plentiful, but there is no D₂O.  Bob grows up on Earth₁, where he forms beliefs, etc. about "water" as a result of interacting with D₂O.  Bill grows up on Earth₂, where he develops the exact same set of beliefs, etc. about "water" as Bob, but based upon interacting with H₂O.  If one is a narrow functional role theorist (using only causal connections "internal" to the cognizer), then the two men must have identical belief content when thinking about "water".  They either form beliefs, make inferences, etc., using states that represent what we would describe using the disjunction, "H₂O or  D₂O", or their states represent both H₂O and also D₂O (as distinct entities) simultaneously.  Most philosophers consider the latter even less intuitively plausible than the former.
 

Long arm or two factor theories can distinguish Bill’s and Bob’s beliefs since they include causal connections to environmental objects and/or properties.  However, suppose that Bob also has the beliefs that "water is H₂O," that "I live on Earth₂," and "Earth ₂ has only H₂O on it’s surface."    Is Bob representing "water" as  D₂O, but forming a false belief about the chemical structure of D₂O?  Or, is he representing "water" as H₂O and forming false beliefs about the D₂O he finds in his environment.  Critics assert that functional role semantics lacks the resources to disambiguate such scenarios.
 

Representational Structure
Finally,  Fodor and LePore (1992), Fodor and McLaughlin (1981), and Fodor and Plysyhyn (1988) raise the objection that functional role semantics seems to violate truths about the structure of language and thought like compositionality and systemativity.  Compositionality is the theory that the meaning of a complex expression in a language results from the meanings of its constitutive elements.   Compositionality plays an central role in many linguistic theories, since its supposition for both language and thought provides a fairly straightforward explanation of the human ability to grasp an enormous number of different thoughts of varying complexity and their corresponding linguistic expressions.  For instance, because we understand the individual elements like "cup" and "coffee", we understand the complex expressions "cup of coffee," "hot coffee," "coffee gives me the shakes," etc..  One explains our understanding by noting that the meaning of these complex sentences is built-up from the meaning of their constitutive elements.

Fodor and others claim that the functional role of a complex, non-idiomatic representation is not always a function of the functional roles of its parts. As a result, functional role theories can represent "cup of coffee" without having the concepts and associated inferences of "cup" or "coffee".  This alleged aspect of functional role representation schemes would result in the possibility that one could represent and think about "cup of coffee," but could not represent or think about "iced coffee," "hot coffee," etc..  Nor could one understand or evaluate the sentence, "Coffee is the legal drug for which we exploit the people and natural resources of many third world countries."
 

Block (forthcoming ) has suggested that functional role semanticists can account for compositionality by adopting context-sensitive rules of use for words.  That is, meanings of words can be understood as sets of inferences (functional roles) to to sentences containing the word and sets of inferences from sentences containing the word.  Thus, "cup of coffee" does get its meaning from cup and is consistent with one understanding "iced coffee", etc..  Connectionists with commitments to functional roles and others (Smolensky 1991 and 1991a) have argued that connectionist systems can have constituents satisfying many of the criteria of compositionality without adopting traditional compositional representational frameworks.
 

Causal Theories and Cognitive Science
Cognitive science proceeds in the absence of a resolution of the debate over theories of representation.  However, the adoption of either nomic covariance theories or functional role semantics does shape the research of individual cognitive scientists.  Many important debates in cognitive science have resulted from allegiance to one or the other causal theory.  For example, one aspect of the connectionist vs Turing-compatible approaches computation is that advocates of connectionist frameworks tend to adopt functional role semantics, while advocates of Turing-compatible frameworks tend to adopt nomic covariation.  Similarly, the debate over the nature of mental imagery was drawn along covariance vs functional role lines.  It is widely supposed that the adoption of one or the other theory of mental content by the majority of cognitive scientists will have a profound impact on the field.
   
 

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Other Internet Resources

• A Field Guide to the Philosophy of Mind
• Dictionary of Philosophy of Mind
• Internet Encyclopedia of Philosophy
• Mind/Brain Resources
• Block’s Article on Functional Role Semantics

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