While most people interested in concepts will find much to agree with in this book (Doing without Concepts, Machery Reference Machery2009), it is the eliminativist thesis that will find most resistance. Machery provides analogical cases in psychology such as “emotion” and “memory.” Emotion and memory, it is argued, may prove to be terms referring to a varied set of phenomena, without any identifiable single associated brain system. Similar cases can be found in other sciences – for example, “species” and “planet.” The concept of species is problematic because there is not always a clear criterion for differentiating one species from another; instead biological laws describe the distribution of genes over populations of individuals (Mayr Reference Mayr1982). While problems of definition mean that “species” is not a well-defined term in biology, it would, however, be hard to imagine biological discourse without it. There are just too many general truths that need to be expressed. Similarly, astronomers ran into trouble with the designation of Pluto as a planet, given the discovery of other large orbiting bodies that had been labeled as asteroids. But the term still has a referential meaning. Science needs more loosely defined general referring expressions in addition to the carefully defined terms that figure in theories. I argue that cognitive science still needs the notion of “concept,” even if it proves multifaceted and hard to define satisfactorily.

Machery's argument rests on there being three distinct forms of knowledge that are recruited by default by cognitive processes: namely, prototypes (P), exemplars (E), and theories (T). The danger of eliminating the notion of concept is that the importance of the relations between these forms of knowledge risks being underplayed. First, there is the obvious point that the P, E, and T representations (let's call them PET) of dog all refer to the same class – they are broadly co-referential (give or take some differences in categorization resulting from exceptional contexts). What makes them co-referential is the fact that they represent the same concept. Without a notion of concept, it is hard to explain why they co-refer.

More importantly, the term “concept” is needed as part of an account of the many situations in which the PET systems interact. How does one discuss concept combination, including the formation of composite prototypes, the importing of exemplar knowledge, and the coherence checking of the result through background theory, if one cannot have the integrative term “concept” to specify just what it is that is being combined. The combination occurs at the concept level, and the description of the processes involved then requires elaboration in terms of the PET systems. Similarly, in concept learning, we need an overarching notion of concept in order to describe how PET systems interact. Experiential concepts like DOG or CUP may first be learned by a child through interacting with individuals encountered in everyday life. When a variety of individuals are known, and it is necessary to learn to use the words “dog” and “cup” correctly, then prototypes may be formed, enabling generalization to other individuals, discrimination of other classes, and the accumulation of generic knowledge. As the child then develops wider knowledge, the prototype notion of DOG may be supplemented by theoretically driven concepts like mammal or species, and by essentialist ideas about the causal properties of biological kinds, or the need to defer to expert opinion about correct classification.

Far from aiding scientific advance, treating the PET systems as largely independent of each other may impede investigation of the important ways in which information is transferred between them. It can also be argued that the three systems are not as easily distinguished as Machery would require. Consider prototypes and exemplars. Machery agrees that much of the research and debate concerning prototypes and exemplars has been directed at a very restricted form of behavior, namely, learning to classify simple geometrical shapes in a laboratory setting where the categories to be learned are not easily distinguished without extensive training. Even in this arcane area of psychology, there is considerable evidence that under different conditions people will either learn individual exemplars or will abstract prototypes (Smith & Minda Reference Smith and Minda1998). If we move to the more “conceptual” domain of natural language terms, then the question of prototype versus exemplar models hardly arises. For example, Storms et al. (Reference Storms, De Boeck and Ruts2000) have investigated whether typicality in superordinate categories like FISH, FRUIT, or FURNITURE is best predicted by similarity to the category prototype or by similarity to “exemplars.” But in this case the exemplars are simply prototypes defined at a more specific level (e.g., CHAIR and TABLE). So the question is not which of two distinct systems is driving the behavior, but rather which level of abstraction is involved within a single representational system. Some concepts do have genuine exemplars – the concept of “Beethoven Symphony” to a musician will be heavily dependent on knowledge of the nine exemplars. But there will be a close link between knowledge of the exemplars and generalized knowledge about the typical structure and expressive vocabulary found in the works.

Likewise, there has been a rapprochement between prototype and theory-based elements of concepts. In discussing the notion of prototype (Hampton Reference Hampton1998), I have proposed that the distinguishing feature of prototype representations is that they represent the center of a class and not its boundary. It is this fact that gives rise to category vagueness, typicality gradients, the lack of explicit definitions, and the preponderance of generic (rather than necessary) features in people's accounts of the content of the concept. The notion of prototype as a form of schema is therefore free to be supplemented by causal connections within the representation resulting in a structured frame representation (Barsalou & Hale Reference Barsalou, Hale, van Mechelen, Hampton, Michalski and Theuns1993). Mutability and centrality of properties, modal judgments of necessity, and dissociations between similarity-based typicality and theory-based categorization can all be accommodated within this single representational system.

In short, it is too soon to be counseling despair about integrating prototype, exemplar, and theory-based representations into a coherent account of the concept of concept.