Edouard Machery (in Doing without Concepts, Machery Reference Machery2009, p. 12) claims that psychologists (including theory-theorists) take concepts to be “bodies of knowledge that are used by default in the processes underlying the higher cognitive competences” (p. 11). According to Machery's gloss, default knowledge about, for example, dogs is the knowledge that is “preferentially available” (p. 11) and “spontaneously comes to mind” (p. 12) in most contexts in which we make judgments about dogs. People's knowledge about a category is not exhausted by their default knowledge, but their non-default (background) knowledge is less easily retrievable and is used only when default knowledge is insufficient for the task at hand. Machery suggests that whether or not a subject's judgment about x provides evidence about the content of her default body of knowledge relative to x depends (at least partly) on whether or not she made the judgment under time pressure. Thus, he notes in his Précis (target article, sect. 3, para. 8), the fact that under no time pressure people may retrieve a representation of a cheetah that makes the sentence “A man can outrun a cheetah” true is no evidence that this representation belongs to their default knowledge rather than to their background knowledge about cheetahs. In situations with no time pressure, people can and do retrieve information from their background knowledge.
This turns out to be crucial when we consider the nature of the theory-theorists' experiments. There is a stark contrast between the kinds of experimental tasks relied upon by, say, prototype-theorists on the one hand and theory-theorists on the other hand. Prototype theorists have usually relied upon experimental tasks in which subjects were instructed, for example, to list properties associated with a category in a short time period or make categorization judgments under explicit time pressure (see, e.g., Hampton Reference Hampton1979; Rosch & Mervis Reference Rosch and Mervis1975). By contrast, many of the experimental tasks designed by theory-theorists do not involve any element of time pressure. Consider, for instance, Rips's (Reference Rips, Vosniadou and Ortony1989) famous pizza experiment. As Smith and Sloman (Reference Smith and Sloman1994) have rightly noted, “there was no mention of speed in Rips' instructions” (p. 380). Or consider Keil's (Reference Keil1989) transformation experiments, in which subjects were asked to make judgments about the biological membership of an animal that has undergone unusual transformations. Nothing in Keil's text indicates that subjects had to make their categorization judgments under any particular time pressure.
This raises two issues for Machery's discussion of the theory-theory. First, because Rips's and Keil's experimental tasks did not involve any element of time pressure, they do not show that the knowledge retrieved by subjects to solve these tasks belongs to their “default knowledge” in Machery's sense. Subjects might have retrieved information from their background knowledge to make their categorization judgments. (Given the unusual nature of the tasks they were asked to solve, this would not be surprising). However, theory-theorists take Rips's and Keil's experiments to provide crucial insights into the nature and structure of concepts. If theory-theorists assume concepts to be default bodies of knowledge, then they have misinterpreted Rips's and Keil's results. A more charitable hypothesis is that, pace Machery, theory-theorists do not consider that being used by default in higher-level cognitive competences is a necessary condition for a piece of information to count as conceptual knowledge. This hypothesis is supported by some of the theory-theorists' own claims. For example, both Murphy and Medin (Reference Murphy and Medin1985, p. 296) and Gelman (Reference Gelman2003, p. 244) take theories to be concepts, but allow that in many contexts, subjects rely by default on prototypical features to make routine and quick categorization judgments, and retrieve theoretical information only when prototypical information is insufficient for the task at hand.
Here is the second issue. Machery (Reference Machery2009, pp. 52, 119) contends that for most categories, our default knowledge includes a theory of that category, and that theory-like default bodies of knowledge are associated with a distinct kind of categorization process. He mentions Rips's and Keil's results in support of this claim (pp. 183–87). However, these experiments do not support Machery's contention, since they are consistent with the claim that theories belong to background rather than to default knowledge. Moreover, the literature generated by Rips's results partly disconfirms Machery's claim. Thus, Smith and Sloman (Reference Smith and Sloman1994, pp. 379–80) failed to replicate Rips's results when they instructed subjects to make their categorization judgments quickly. This suggests that the theoretical information on which subjects relied in Rips's original experiment did not belong to their default knowledge.
Now, some experimental results mentioned by Machery do support the idea that default bodies of knowledge include theoretical information. Thus, Luhmann et al. (Reference Luhmann, Ahn and Palmeri2006; cited in Machery Reference Machery2009, p. 186) have shown that subjects can use causal knowledge to make categorization judgments even under time pressure. In the learning phase of the experiment, subjects learned about the causal relations between various features of fictional animals. In a subsequent categorization phase, subjects relied upon this causal knowledge to make categorization judgments, even when they were instructed to respond as quickly as possible. This is evidence that their default knowledge about those fictional animals included causal (hence theoretical) knowledge. However, as Luhmann et al. argue, their results are consistent with (and according to them, even support) the idea that their subjects' theory-driven categorization process was not “qualitatively different from traditional similarity-based processes based on weighted feature matching” (2006, p. 1104): Subjects may simply have assigned strong weights to causal features when they first learned the category, and later used those features weights in a simple similarity computation when they made categorization judgments. Thus, these results do not support Machery's claim (2009, p. 119) that theory-like default bodies of knowledge are used in a categorization process similar to scientific reasoning and different in kind from the categorization processes associated with, for example, prototypes.
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Edouard Machery (in Doing without Concepts, Machery Reference Machery2009, p. 12) claims that psychologists (including theory-theorists) take concepts to be “bodies of knowledge that are used by default in the processes underlying the higher cognitive competences” (p. 11). According to Machery's gloss, default knowledge about, for example, dogs is the knowledge that is “preferentially available” (p. 11) and “spontaneously comes to mind” (p. 12) in most contexts in which we make judgments about dogs. People's knowledge about a category is not exhausted by their default knowledge, but their non-default (background) knowledge is less easily retrievable and is used only when default knowledge is insufficient for the task at hand. Machery suggests that whether or not a subject's judgment about x provides evidence about the content of her default body of knowledge relative to x depends (at least partly) on whether or not she made the judgment under time pressure. Thus, he notes in his Précis (target article, sect. 3, para. 8), the fact that under no time pressure people may retrieve a representation of a cheetah that makes the sentence “A man can outrun a cheetah” true is no evidence that this representation belongs to their default knowledge rather than to their background knowledge about cheetahs. In situations with no time pressure, people can and do retrieve information from their background knowledge.
This turns out to be crucial when we consider the nature of the theory-theorists' experiments. There is a stark contrast between the kinds of experimental tasks relied upon by, say, prototype-theorists on the one hand and theory-theorists on the other hand. Prototype theorists have usually relied upon experimental tasks in which subjects were instructed, for example, to list properties associated with a category in a short time period or make categorization judgments under explicit time pressure (see, e.g., Hampton Reference Hampton1979; Rosch & Mervis Reference Rosch and Mervis1975). By contrast, many of the experimental tasks designed by theory-theorists do not involve any element of time pressure. Consider, for instance, Rips's (Reference Rips, Vosniadou and Ortony1989) famous pizza experiment. As Smith and Sloman (Reference Smith and Sloman1994) have rightly noted, “there was no mention of speed in Rips' instructions” (p. 380). Or consider Keil's (Reference Keil1989) transformation experiments, in which subjects were asked to make judgments about the biological membership of an animal that has undergone unusual transformations. Nothing in Keil's text indicates that subjects had to make their categorization judgments under any particular time pressure.
This raises two issues for Machery's discussion of the theory-theory. First, because Rips's and Keil's experimental tasks did not involve any element of time pressure, they do not show that the knowledge retrieved by subjects to solve these tasks belongs to their “default knowledge” in Machery's sense. Subjects might have retrieved information from their background knowledge to make their categorization judgments. (Given the unusual nature of the tasks they were asked to solve, this would not be surprising). However, theory-theorists take Rips's and Keil's experiments to provide crucial insights into the nature and structure of concepts. If theory-theorists assume concepts to be default bodies of knowledge, then they have misinterpreted Rips's and Keil's results. A more charitable hypothesis is that, pace Machery, theory-theorists do not consider that being used by default in higher-level cognitive competences is a necessary condition for a piece of information to count as conceptual knowledge. This hypothesis is supported by some of the theory-theorists' own claims. For example, both Murphy and Medin (Reference Murphy and Medin1985, p. 296) and Gelman (Reference Gelman2003, p. 244) take theories to be concepts, but allow that in many contexts, subjects rely by default on prototypical features to make routine and quick categorization judgments, and retrieve theoretical information only when prototypical information is insufficient for the task at hand.
Here is the second issue. Machery (Reference Machery2009, pp. 52, 119) contends that for most categories, our default knowledge includes a theory of that category, and that theory-like default bodies of knowledge are associated with a distinct kind of categorization process. He mentions Rips's and Keil's results in support of this claim (pp. 183–87). However, these experiments do not support Machery's contention, since they are consistent with the claim that theories belong to background rather than to default knowledge. Moreover, the literature generated by Rips's results partly disconfirms Machery's claim. Thus, Smith and Sloman (Reference Smith and Sloman1994, pp. 379–80) failed to replicate Rips's results when they instructed subjects to make their categorization judgments quickly. This suggests that the theoretical information on which subjects relied in Rips's original experiment did not belong to their default knowledge.
Now, some experimental results mentioned by Machery do support the idea that default bodies of knowledge include theoretical information. Thus, Luhmann et al. (Reference Luhmann, Ahn and Palmeri2006; cited in Machery Reference Machery2009, p. 186) have shown that subjects can use causal knowledge to make categorization judgments even under time pressure. In the learning phase of the experiment, subjects learned about the causal relations between various features of fictional animals. In a subsequent categorization phase, subjects relied upon this causal knowledge to make categorization judgments, even when they were instructed to respond as quickly as possible. This is evidence that their default knowledge about those fictional animals included causal (hence theoretical) knowledge. However, as Luhmann et al. argue, their results are consistent with (and according to them, even support) the idea that their subjects' theory-driven categorization process was not “qualitatively different from traditional similarity-based processes based on weighted feature matching” (2006, p. 1104): Subjects may simply have assigned strong weights to causal features when they first learned the category, and later used those features weights in a simple similarity computation when they made categorization judgments. Thus, these results do not support Machery's claim (2009, p. 119) that theory-like default bodies of knowledge are used in a categorization process similar to scientific reasoning and different in kind from the categorization processes associated with, for example, prototypes.
ACKNOWLEDGMENT
I thank Alvin Goldman for helpful advice and comments.