R2. Clarifications

Before addressing the substantive criticisms made by the commentators, I should briefly clarify a few misunderstandings. Hayes & Kearney misinterpret my concerns with the term concept. I do not recommend that concept be eliminated from cognitive scientists' classificatory scheme because of the context-sensitivity of knowledge retrieval from long-term memory. (By contrast, Vlach, Krogh, Thom, & Sandhofer [Vlach et al.] recommend eliminating concept on precisely these grounds – more on this in section R3.) Indeed, I concur with Hayes & Kearney that behavioral and neuroimaging evidence shows that, while knowledge retrieval is indeed context-sensitive, some knowledge is also retrieved in a context-insensitive manner (Machery, forthcoming; see discussion in sect. R3), as I explained in two distinct places of DwC (sects. 1.4.1 and 8.1.1). In fact, I propose to identify concepts with those bodies of knowledge that are retrieved in a context-insensitive manner. I also agree with Hayes & Kearney that models of cognitive processes that assume the existence of such context-insensitive bodies of knowledge are compatible with the contextual variation observed in experimental tasks. So, what are, for me, the grounds for eliminating concept? Instead of being concerned with flexibility and context-sensitivity, I suggest eliminating concept because, failing to pick out a natural kind, this term does not fulfill its classificatory function (see sects. R9.1 and R9.2), and because keeping this term would have some important drawbacks and very few benefits (see sects. R9.4 and R9.5).

Vlach et al. object to my criticism of the anti-representationalist approaches in cognitive science, but they seem to misunderstand the claim made by these approaches (illustrated, e.g., by Rodney Brooks's work and by some versions of the dynamical systems theory), namely, that cognitive science should explain behavior without ascribing to organisms representations of their environment. Thus, contrary to what Vlach et al. seem to believe, anti-representationalist approaches to cognitive science do not merely reject the idea of enduring representations – namely, representations stored in long-term memory; they reject the idea that organisms have any kind of representations, including representations constructed on the fly.

R3. What are concepts?

One of the goals of DwC was to clarify and regiment the slippery notion of concept used in cognitive science. According to the characterization C (introduced and defended in Chapter 1), a concept of x is a body of knowledge about x that is used by default in the processes underlying our higher cognitive competencies when these result in judgments about x. Blanchard, Lalumera, Margolis & Laurence, Markman, Rey, Vlach et al., and Weiskopf raise some questions about this characterization of the notion of concept.

Lalumera objects that C is an incomplete characterization of the notion of concept in cognitive science, but her own discussion belies this claim. Although the notion of a higher cognitive competence was left vague, it is clear that the examples of competencies that, according to her, I ignored (viz., generalization and induction) straightforwardly fall under this notion. Indeed, induction is one of the examples I have repeatedly used to illustrate what higher cognitive competencies are.

Blanchard doubts that the notion of default is an appropriate way of cashing out the notion of concept used in cognitive science. Noting that many experiments meant to support the theory theories of concepts are not run under time pressure, he concludes that either theory theorists do not view their work as bearing on concepts – which, I agree with Blanchard, is dubious – or the notion of default fails to capture the notion of concept they use.

Blanchard's objection is an excellent occasion to clarify the notion of default (see also Machery, forthcoming). On my view, three properties are characteristic of the bodies of knowledge retrieved by default: speed, automaticity, and context-independence. The bodies of knowledge retrieved by default come to mind quickly; their retrieval does not depend on one's intentional control (although they may also be intentionally retrieved); and they are retrieved in all contexts. Of these three properties context-independence is the essential one, while speed and automaticity are likely effects of context-independence: Because a body of knowledge is retrieved in a context-insensitive manner, its retrieval from memory might be simpler and thus faster, and it can be automatized. On my view, being retrieved quickly – for example, being retrieved under time pressure in an experimental context – is evidence, but not a necessary condition, for being retrieved by default. Thus, experimental tasks that do not involve time pressure can be used to examine people's concepts.

Rey criticizes my alleged identification of concepts with the bodies of knowledge used under time pressure (see my response to Blanchard above), and he proposes to identify concepts with those bodies of knowledge we would use if we were to reflect. However, if we were to follow this proposal, psychologists working on concepts would be unable to explain how people categorize, make inductions, understand words, and so on, in most circumstances.

Like Barsalou (Reference Barsalou, Collins, Gathercole and Conway1993) and Prinz (Reference Prinz2002), Vlach et al. hold that concepts are temporary constructs in working memory on the grounds that there is “a great variability of the knowledge that is brought to bear in a particular task.” I concur with Vlach et al. that the knowledge brought to bear on a given task is influenced by context; indeed, I explicitly acknowledge this variability in DwC, and the useful references they give in their commentary provide further evidence of this variability. However, as shown in DwC and in the Précis, several remarkable behavioral and neuroimaging studies also support the claim that some bodies of knowledge are retrieved by default (Barsalou Reference Barsalou1982; Weisberg et al. Reference Weisberg, van Turrennout and Martin2007; Whitney et al. Reference Whitney, McKay, Kellas and Emerson1985). Vlach et al. do not address this body of evidence and provide no reason to doubt the conclusion it seems to support.

Other findings provide further evidence for the claim that some bodies of knowledge are retrieved by default. Although their goal was to highlight the context-sensitivity of knowledge retrieval, Hoenig et al. (Reference Hoenig, Sim, Bochev, Herrnberger and Kiefer2008) have shown that brain areas involved in representing actions or physical manipulations are automatically activated in a feature verification task when the question concerns the appearance of a tool, while, conversely, the brain areas involved in representing visual appearances are automatically activated when the question concerns the movement associated with a natural object. James and Gauthier (Reference James and Gauthier2003) have similarly shown that auditory areas and areas dedicated to the processing of movements are activated by the mere visual presentation of novel objects (greebles) when participants have respectively been trained to recognize the sounds of these objects and their movements. In both experiments, knowledge that is not relevant to the tasks at hand is accessed in a context-insensitive manner.

Furthermore, the variability of the knowledge used in different contexts is consistent with the fact that knowledge retrieval from long-term memory is partly context-insensitive. Indeed, Hayes & Kearney discuss several models that account for the variability while assuming that some bodies of knowledge are retrieved by default (see also sect. 1.4.1 of DwC).

Both Margolis & Laurence and Weiskopf concur that defining concepts as the constituents of thoughts provides a better characterization of the notion of concept than C. Before discussing this proposal, note that, contrary to what Weiskopf claims, I do not deny that concepts are the constituents of thoughts. Rather, I insist that concepts should not be defined as the constituents of thoughts (sect. 1.4.3 of DwC).

Margolis & Laurence and Weiskopf propose to clarify the notion of a constituent of thought by appealing to the language-of-thought hypothesis. However, it would be a mistake to build an empirical hypothesis as controversial as this in the very notion of concepts since the validity of the work of cognitive scientists working on concepts (e.g., their account of the bodies of knowledge retrieved when we categorize or draw an induction as well as their accounts of the categorization or induction processes) does not hang on the truth of the language-of-thought hypothesis.

Finally, there is little benefit to defining concepts as constituents of thoughts since this definition does not cast light on cognitive scientists' research. While Margolis & Laurence mention numerous psychologists who do characterize concepts as constituents of thoughts (Carey, etc.), they do not show that this characterization plays any role in these psychologists' actual empirical work on concepts.

Weiskopf mentions the need to explain the productivity of human thought (see also Hill Reference Hill2010). This suggests that he does not simply define concepts as constituents of thoughts. Instead, for him, a body of knowledge is a concept only if it can combine freely with any other body of knowledge (i.e., only if it meets Evans's [Reference Evans1982] generality constraint). First, it is not clear that productivity is among the explananda of a psychological theory of concepts, but I will not press this point here (Machery Reference Machery2010). Rather, I propose that Weiskopf's definition is arbitrary. If concepts are defined this way, organisms that are able to combine all bodies of knowledge freely (as humans do according to Weiskopf) have concepts, whereas organisms that are able to combine many such bodies, but not all, do not, even if the bodies of knowledge in the former and latter kinds of organism are very similar.

Here is another way of illustrating the arbitrariness of Weiskopf's proposal. Suppose we humans have some bodies of knowledge that are used in categorization, induction, and the like, in almost the same way as our other bodies of knowledge. For example, they could be prototypes, and they could be used in similarity-based processes. But, while the other bodies of knowledge can be combined freely, these prototypes can only be combined with a limited number of other prototypes (perhaps because they belong to a modular cognitive system). Weiskopf would conclude that these prototypes are not concepts since they cannot combine freely with all the other bodies of knowledge, but this is the wrong conclusion to draw. Instead, the similarities between these prototypes and the other bodies of knowledge should lead us to conclude that they are concepts and to reject Weiskopf's proposal that a body of knowledge counts as a concept only if it can combine with every other body of knowledge.

Rey argues that my characterization of concept entails that two individuals or even a single individual at two different times cannot have the same concept. However, it is incorrect that a single individual at two different times cannot have the same concept, since a given concept can remain the same although its parts (viz., the elements of knowledge that are by default retrieved from long-term memory) change, exactly as objects remain the same despite their parts changing (Machery Reference Machery2010). It is true that, given my characterization of concept, different individuals are likely to have different concepts (e.g., different concepts of dogs), but I think that this is a clear virtue, since this explains why they categorize differently and make different inductions.

Finally, Markman argues that it is a mistake to characterize psychological constructs, such as the notion of concept, by means of particular cognitive competencies and experimental tasks since adequate psychological constructs should explain performance in a range of tasks; and he regrets that I did not pay attention to a broader range of competences and tasks. I agree with Markman's argument. Although DwC examined only three cognitive competencies and focused on a few psychological tasks, the proposed characterization of concept – namely, C – is consistent with Markman's point.

R4. Philosophers and psychologists on concepts

Another goal of DwC was to show that, although philosophers and psychologists use the term concept and develop theories of concepts, psychological and philosophical theories of concepts are really about different things. As a result, many criticisms of psychological theories of concepts by philosophers (and vice versa) are empty. Edwards, Margolis & Laurence, Rey, and Schneider disagree with this claim. Keil also seems to assume that philosophical and psychological theories of concepts are about the same thing, but does not press this point.

Edwards and Margolis & Laurence are right to claim that the fact that psychologists and philosophers have different explanatory interests does not entail that they are theorizing about different things, because they could be theorizing about different aspects of the same phenomenon.

I deny the univocity of concept across philosophy and psychology on the following grounds. Generally, in philosophy of science, a candidate explication of a scientific term (e.g., ether, force) is taken to be a failure if it entails that what scientists say when they use this term is typically mistaken. This is in fact a commonsense idea: If my interpretation of what someone means by a particular word entails that most what she says when she uses this word is false, my interpretation is probably mistaken. Applied to the notion of concept in cognitive science, a satisfactory explication of this notion should not entail that psychologists' claims about concepts are literally false. C, but not Margolis & Laurence's characterization, meets this constraint. (A similar objection applies to Rey's and Edwards's characterizations.) Since Margolis & Laurence propose that the bodies of knowledge psychologists have been focusing on (viz., prototypes, exemplars, etc.) belong to the processing structure of concepts (whatever that is), they are bound to claim that psychologists are literally mistaken when they say that concepts are prototypes or exemplars (etc.).

Margolis & Laurence take the mutual influence of philosophers and psychologists to be evidence that psychologists and philosophers are talking about the same thing when they theorize about concepts, but I am not swayed by this argument. First, I am more impressed by how often psychologists and philosophers talk past each other when they exchange arguments about concepts than by how useful these exchanges have been. Second, the extent to which philosophers and psychologists have fruitfully influenced each other is perfectly consistent with the idea that they do not theorize about the same thing when theorizing about concepts. Cell biologists and physicists working on quantum mechanics do not theorize about the same thing, but the former are usefully appealing to the theories and findings of the latter (e.g., Collini et al. Reference Collini, Wong, Wilk, Curmi, Brumer and Scholes2010).

Because I hold that philosophers and psychologists who theorize about concepts are not talking about the same thing, I find Edwards's and Rey's critiques puzzling. Clearly, it is important to understand better how concepts refer, but this is not one of the explananda of the theories developed by psychologists theorizing about concepts. Furthermore, as argued in section 2.4 of DwC, the kind of arguments exchanged by philosophers, which often rely on intuitions about what concept an individual in a particular circumstance possesses or fails to possess, or about whether two individuals have the same belief (e.g., Burge Reference Burge1979), seems unlikely to be appropriate for determining how concepts refer.

Schneider notes that psychologists' findings about how we categorize, draw inductions, and so forth, can be co-opted by some philosophical theories of concepts – those that individuate concepts by means of the functional role of mental symbols. While correct, this observation does not undermine the claim that psychologists and philosophers tend to theorize about different things when they theorize about concepts. Similarly, while cell biologists use biochemists' findings, biochemists and cell biologists are not developing theories about the same processes.

R5. Rejecting the heterogeneity of the class of concepts

To my surprise, few commentaries objected to the claims that there are several kinds of concepts, and that prototypes, exemplars, and theories are among these kinds. Strohminger & Moore and Rey seem even to have found this claim entirely unsurprising. However, I worry that this lack of resistance is due to a confusion between two different claims: (1) that prototypes, exemplars, and theories are three distinct kinds of concept; and (2) that our long-term memory includes prototypes, exemplars, and theories. These two claims are not identical since one could grant that we have, say, exemplars and theories, but insist that concepts are prototypes (e.g., Hampton Reference Hampton, Hahn and Ramscar2001) or that we have prototypes and exemplars, but insist that concepts are really theories. While Claim 2 is indeed not very controversial, Claim 1 is less obviously correct.

Hayes & Kearney, Harnad, and Hampton are the only ones to raise doubts about the heterogeneity of concepts. Harnad rejects the idea that the bodies of knowledge we use in higher cognitive tasks are prototypes or exemplars. Rather, sensorimotor processes play a central role in cognition: They enable living creatures to navigate the world by making object identification and appropriate action possible. There is no doubt that such sensorimotor processes exist since recognition must involve them, but these processes cannot underwrite the bulk of cognition. Like behaviorists and like some roboticists (see Machery Reference Machery2006b, on Harvey), Harnad underestimates the complexity of higher cognition when he proposes that the processes that can explain perceptual and motor processing can scale up to higher cognition. Appealing to words, as Harnad does, does not help much since words have to be understood and mapped onto bodies of knowledge in long-term memory.

Hampton contends that the distinction between exemplars and prototypes breaks down for at least some categories since the exemplars of superordinate categories, such as the category of vehicles, are prototypes of subordinate categories, such as the category of cars (see also Malt, forthcoming). However, superordinate categories could be represented by representations of particular cars, planes, bikes, and so on, rather than by prototypes of cars, plans, bikes, et cetera. This is naturally an empirical question, and Hampton might well be right. Supposing he is right, it would nonetheless be a mistake to say, as he does, that the exemplars of superordinate categories are prototypes of the subordinate categories. Rather, using the term exemplar to refer only to representations of individuals, one should say that superordinate categories are represented by sets of prototypes of subordinate categories.

In any case, Hampton's interesting comment brings to the fore a shortcoming of DwC – the neglect of superordinate concepts and the focus on basic-level categories (e.g., dogs). It might be that the heterogeneity of conceptual representations is even larger than proposed in DwC, with superordinate categories being represented differently from basic-level and subordinate categories. Importantly, far from undermining the crucial message of the book, this outcome would reinforce it: It is hopeless to look for a theory of conceptual representations that applies to all default bodies of knowledge.

Hayes & Kearney defend the received view. They contend that exemplar models of a range of phenomena outperform prototypes models (see also Zaki & Cruz), and that the role of theories can naturally be included in exemplar models (on this latter point, see also Yermolayeva & Rakison). But some of the studies they themselves cite in fact undermine this claim. Far from providing evidence that categorization can be explained by means of a single kind of default bodies of knowledge, Allen and Brooks (Reference Allen and Brooks1991) provided evidence that, in at least some circumstances, we have two distinct representations of a single category (a rule and a set of exemplars) and that these representations can lead to conflicting categorization judgments. Smith et al. (Reference Smith, Patalano and Jonides1998) have replicated these findings, and provided evidence that two neural networks are involved in each categorization judgment. Furthermore, exemplar models seem able to explain the empirical findings about concepts only if one takes exclusively into consideration the category-learning studies that involve artificial stimuli such as patterns of points. Research on the knowledge of expert physicians (reviewed in Norman et al. Reference Norman, Eva, Brooks, Hamstra, Ericsson, Charness, Feltovich and Hoffman2006) shows, for instance, that during their training in medical school, physicians acquire different types of bodies of knowledge that are largely independent from one another.

Further, for Hayes & Kearney, the role of theories in cognition is indirect: They influence which exemplars are learned in category-learning tasks or which exemplars are retrieved from long-term memory (which explains perhaps why Hayes & Kearney prefer to speak of prior knowledge instead of theories). However, a less partial review of the literature suggests that the use of theories is not so limited, and that causal theories are directly used to categorize and to make inductions (Chs. 6 and 7 of DwC).

Finally, in DwC, I argued that simplicity can be used to choose between scientific hypotheses in a domain of inquiry (e.g., in psychology) only if past evidence inductively supports the belief that in this domain simpler hypotheses tend to be better supported than more complex hypotheses. By contrast, Zaki & Cruz argue that simplicity should always be preferred on the grounds that models with more free parameters fit better a given set of data points than models with less free parameters; and they conclude that, everything else being equal, we should prefer a theory that posits a single kind of concept to a theory that posits several distinct kinds of concept. Although the question cannot be resolved in a few words, their argument should be resisted for two reasons. First, it is not necessarily the case that simpler models fit better than more complex ones when fit is evaluated by cross-validation since models with more parameters can overfit. Second, model fitting provides a poor, albeit common (e.g., Forster & Sober Reference Forster and Sober1994), analogy for understanding the use of simplicity as a criterion for theory choice. More complex theories are not necessarily better supported than simpler theories since they often have empirical implications that simpler theories simply do not have. For instance, the heterogeneity hypothesis – but not (e.g.) prototypes theories – predicts that in at least some cases people's categorization (or induction) judgments are going to be slower or less reliable because, for example, the prototype-based and theory-based categorization (or induction) processes conflict with one another (for consistent evidence, see Allen & Brooks Reference Allen and Brooks1991; Kulatanga-Moruzi et al. Reference Kulatanga-Moruzi, Brooks and Norman2001; Regehr et al. Reference Regehr, Cline, Norman and Brooks1994; Smith et al. Reference Smith, Patalano and Jonides1998; and see sects 5.1.5, 6.6, and 7.1.5 of DwC).

R6. Can prototypes, exemplars, and theories be coreferential?

While I proposed that we often have several coreferential concepts – for example, we might have a prototype of dogs, a set of exemplars about dogs, and a theory of dogs – Hampton, Jacobson, and Margolis & Laurence doubt that prototypes, exemplars, and theories can co-refer.

In DwC, I intentionally refrained from proposing a theory of how bodies of knowledge such as prototypes, sets of exemplars, and theories denote (see Edwards's and Rey's commentaries), and this is not the place to propose one. However, for present purposes, it is sufficient to note that, according to several influential theories of reference, a prototype, a set of exemplars, and a theory can be coreferential. Consider, for instance, Fodor's informational semantics (e.g., Fodor Reference Fodor1990). According to this view, roughly, a concept refers to the property that it is nomologically linked to. As argued convincingly by Prinz (Reference Prinz2002), informational semantics can naturally be combined with prototype theories: A prototype of dogs refers to dogs because its occurrence (i.e., its retrieval from long-term memory) is nomologically linked to the presence of dogs in the cognizer's environment. Informational semantics can similarly be combined with theory theories and with exemplar theories. Thus, it is perfectly possible for a prototype, a set of exemplars, and a theory to be coreferential.

Jacobson and Margolis & Laurence assert, mistakenly, that a prototype, a set of exemplars, and a theory cannot be coreferential because they fail to distinguish reference and categorization (on this distinction, see sect. 2.2.2 of DwC). The fact that objects can be miscategorized (e.g., a wolf can be misclassified as a dog) shows that reference differs from categorization. Indeed, categorization judgments could not be mistaken if every object that is categorized as an x (e.g., as a dog) really belonged to the extension of the concept of x (e.g., the concept of dog). Because reference differs from categorization, the fact that prototype-based and theory-based categorization processes can occasionally classify some objects differently (see the examples in sect. 3.3 of DwC and in Machery & Seppälä, forthcoming) does not entail that a prototype and a theory cannot be coreferential.

R7. Should the heterogeneity hypothesis be broadened?

Couchman, Boomer, Coutinho, & Smith (Couchman et al.), Dove, and Khemlani & Goodwin argue that the heterogeneity hypothesis fails to capture the extent to which concepts form an heterogeneous kind, and they propose to extend the idea that concepts divide into very different kinds in two distinct directions. I am sympathetic to this kind of proposal: One of the important questions to be addressed by future research on knowledge representation is whether prototypes, exemplars, and theories exhaust the fundamental kinds of default bodies of knowledge (see the conclusion of DwC).

Dove proposes that, in addition to distinguishing prototypes, exemplars, and theories, it is necessary to distinguish at least two types of format: amodal and modal (the Representational Heterogeneity Hypothesis). Contra Barsalou, Prinz, and others, Dove agrees with me that not all concepts have a perceptual format (Dove Reference Dove2009; Machery Reference Machery2006c; Reference Machery2007; forthcoming). However, following the dual-coding tradition (Paivio Reference Paivio1991), he also holds that some concepts have such a format. While the evidence reviewed by Dove is surely suggestive, I remain to be convinced. It is again important to keep in mind the distinction (which is apparently not challenged by Dove) between concepts and the knowledge used in higher cognition: Concepts are just a subset of the knowledge used in higher cognition (see sect. 1.1 of DwC and sect. R3 here for a discussion of how to draw the distinction). There is no doubt that we use perceptual representations to solve some tasks, and it is plausible indeed, as Dove argues, that dedicated cognitive systems are used for this purpose. However, this does not entail that these representations are concepts since they might only be used in particular circumstances, in a context-sensitive manner.

Khemlani & Goodwin propose to add two other kinds to the fundamental kinds of concepts: rules and generic representations. Goodwin's work about conceptual illusions provides some striking evidence that people are able to learn rules that determine category membership. However, as I explained in section 4.1.4 of DwC, the concern with the rule-based approach to concepts is not that people are unable to learn and apply rules, but rather that natural categories, outside of contrived laboratory conditions, do not have the definitions that rule-based accounts assume. In contrast to rules, it is extremely plausible that people store some knowledge about generics, as Prasada's work (among others) suggests. In DwC, following many psychologists, I took knowledge of generics and knowledge of causal relations to be constitutive of theories, but, unfortunately, I did not defend this proposal. Khemlani & Goodwin want to distinguish representations of generic information from theories apparently on the grounds that generic knowledge cannot be identified with causal knowledge. However, because generic knowledge and causal knowledge about some x's (e.g., dogs) are plausibly intertwined, it would be a mistake to hold that generic knowledge and theories form distinct kinds of concepts. In the terminology of DwC (sect. 3.3.1; see also sect. R8 here), they seem to be linked (or connected) and coordinated. As a consequence, they should be thought of as parts of the same concept, our theory of dogs, rather than as two distinct concepts. In this sense, theories are true hybrids: They are made of distinct types of knowledge, perhaps used in distinct processes, that are linked and coordinated.

R8. Hybrid theories

Proponents of hybrid theories of concepts agree with some, but not all, tenets of the heterogeneity hypothesis. They propose that the heterogeneous bodies of knowledge about a given category (e.g., dogs) are not distinct concepts, but rather the parts of a single concept. Keil, Gonnerman & Weinberg, Margolis & Laurence, and Scarantino defend hybrid theories against the attack mounted in section 3.3 of DwC. As I understood the notion of part, if two bodies of knowledge A and B are parts of the same concept, using A enables the use of B (A and B are linked or connected), and A and B must not lead to incompatible judgments that are taken to be equally authoritative (A and B are coordinated). Keil, Gonnerman & Weinberg, Margolis & Laurence, and Scarantino all reject Coordination as a necessary condition for two bodies of knowledge to be parts of the same concept. Although Coordination may finally turn out to be an inappropriate way to characterize the notion of conceptual parthood, I will defend it here. Note that, if Coordination is rejected, an alternative characterization of the notion of conceptual parthood should be provided (which Keil fails to do).

Before discussing their key arguments, let me clarify Coordination a bit. Coordination does not state that the parts of a hybrid concept cannot underlie incompatible judgments. This would be an inaccurate way of cashing out the notion of a part of a concept since some well-known hybrid theories of concepts (e.g., Osherson & Smith Reference Osherson and Smith1981) assume that the judgments underwritten by prototypical information can be defeated by (and can thus be incompatible with) the judgments underwritten by theoretical or definitional information. What Coordination excludes is that the parts of a concept give rise to incompatible judgments that are taken to be equally authoritative.

Keil and Gonnerman & Weinberg propose two different arguments purporting to show that Coordination cannot be a necessary condition for distinct bodies of knowledge to count as parts of the same concept. Keil rightly notes that predicates such as “tall” can lead to apparent contradictions: Someone can be tall with respect to some standard and not tall with respect to another standard. He infers that, if Coordination were a necessary condition for conceptual parthood, we would have to conclude, absurdly, that all these judgments involve distinct concepts. However, what is going on in these cases is clearly quite different from what is going on when people both agree and disagree with “Tomatoes are vegetables.” In the former case, when one both agree and disagree with the claim that, say, John is tall, it is not because “tall” is ambiguous: The meaning of “tall” is the same in “John is tall” and “John is not tall.” Instead, one can both agree and disagree with the claim that John is tall because two distinct standards are applied (compared with Tom Cruise, John is tall, but, compared with Shaquille O'Neal, John is not tall). By contrast, one can both agree and disagree with the claim that tomatoes are vegetables because “vegetable” is ambiguous: The meaning of “vegetable” (i.e., the concept this word expresses) is not the same in “Tomatoes are vegetables” and in “Tomatoes are not vegetables.”

Gonnerman & Weinberg note insightfully that the distinct exemplars of, for example, dogs (which, according to me, form a concept of dogs) seem to violate Coordination, which shows that Coordination cannot be a necessary condition for distinguishing concepts. Exemplars of, say, dogs can indeed underlie incompatible judgments – such as, inconsistent categorization judgments – since different exemplars might be retrieved from long-term memory in different circumstances, but it does not follow that these judgments are taken to be equally authoritative (although, to my knowledge, exemplar theorists have said little about this question). Perhaps the judgment underwritten by the larger number of exemplars is taken to defeat the judgment underwritten by the smaller number of exemplars. Although evidence is lacking to evaluate this proposal, it might thus be that exemplars do not violate Coordination.

Scarantino proposes to replace Coordination with weaker conditions, which are satisfied by prototypes, exemplars, and theories, and concludes that these count as parts of concepts rather than as distinct concepts. The main problem with Scarantino's conditions is that they are neither sufficient nor necessary for two bodies of knowledge to be parts of the same concept. Consider, for instance, his first proposal: Two bodies of knowledge are coordinated when the knowledge stored in one of them influences the acquisition of the knowledge stored in the other. A first problem with this proposal is that genuinely distinct concepts meet this condition. For instance, when one forms a body of knowledge about a new animal species, our theoretical body of knowledge about animals in general is likely to influence this acquisition process. A second problem is that the parts of a single concept need not meet this condition. For instance, the elements of knowledge about the typical properties of dogs are parts of the same prototype of dogs, but my knowledge about a typical property of dogs needs not influence the acquisition of my knowledge about another typical property.

Finally, Keil argues that hybrid theories of concepts can account for the findings that I argued undermine them – namely, the fact that people are willing to endorse apparent contradictions such as “Tomatoes are vegetables” and “Tomatoes are not vegetables,” particularly when such sentences are prefaced with hedges such as “in a sense” (see Machery & Seppälä [forthcoming] for some relevant findings and discussion). There are two issues that need to be distinguished here. First, would people be willing to endorse apparent contradictions such as “Tomatoes are vegetables” and “Tomatoes are not vegetables” if they were not prefaced by hedges such as “in a sense”? I suspect that this is the case, but there is no clear evidence for this claim. Second, supposing that people would agree that tomatoes are vegetables and that they are not vegetables even without such edges, hybrid models would then be compatible with people's judgments only if Coordination were rejected. But, if hybrid theorists reject Coordination, they then need to explain why distinct bodies of knowledge about, say, tomatoes are parts of the same concept of tomato instead of being distinct concepts of tomato.

R9. Eliminativism

Most commentators reject the eliminativist conclusion put forward in DwC, even when they agree with the existence of three different types of concepts.