Introduction
A central claim of Machery's Précis (target article) – and of his book, Doing without Concepts (Machery Reference Machery2009) – is that concepts do not constitute a natural kind. Until reading his work on the topic, we would have been inclined to agree. But he has changed our minds. Machery's discussion, when appropriately construed, provides grounds to suppose that concepts do constitute a natural kind.
What is a natural kind?
Though the notion of a natural kind has been characterized many times over, philosophers of science have, in recent years, reached a consensus – or as close to consensus as philosophers ever get – according to which natural kinds are Homeostatic Property Clusters (HPC; Boyd Reference Boyd1991; Machery Reference Machery2005). According to the HPC account, a kind K is natural if:
H1. It is associated with a contingent property cluster: a range of characteristics or symptoms which tend to be co-instantiated by instances of the kind, but need not be genuine necessary conditions for membership.
H2. There is some set of empirically discoverable causal mechanisms or structures – a causal essence – that explains the covariation of these symptoms.
H3. To the extent that there is any real definition of what it is for something to be a member of the kind, it is not the symptoms but the presence of the causal essence producing the symptoms that are definitive of kind membership (Boyd Reference Boyd1989).
This conception of natural kinds is intended to capture the central features of those kinds paradigmatically studied by science. Most importantly, the fact that the existence of property-clusters depends on the operation of an underlying causal essence helps explain why such kinds are typically subsumed by many non-accidental, empirical generalizations (Griffiths Reference Griffiths1997; Machery Reference Machery2005).
Why suppose that concepts constitute a natural kind?
Machery endorses the HPC account, yet he denies that concepts constitute a natural kind. We maintain, however, that if his claims about the cognitive scientist's notion of a concept are correct, then concepts are plausibly a natural kind in the HPC sense. First, consider some of the characteristics that, according to Machery, concepts possess:
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1. Concepts consist in bodies of information.
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2. Concepts are stored in long-term memory, and persist even when not actively deployed.
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3. Concepts are non-proprietary.
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4. Concepts are default representations automatically retrieved from long-term memory.
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5. Concepts are subject to temporal and inter-subjective variation.
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6. Concepts are internally connected.
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7. Concepts are internally coherent.
No doubt other generalizations hold of concepts as such. But even the characteristics 1–7 just listed provide grounds to suppose that concepts are a natural kind. If true, they suggest that concepts satisfy the main conditions imposed by the HPC account. Specifically:
C1: Concepts exhibit a reliably covarying property cluster, including internal coherence, connectedness, persistence, and so on.
C2: The existence of the property cluster depends largely on the operation of an abstractly, functionally characterizable kind of process. Roughly: Most of the properties depend on facts about long-term memory, the operations that it performs, and its relations to other higher cognitive processes.
C3: To the extent that inclusion in the kind, concept, can be defined, it should be the condition of being subject (in the right kind of way) to the relevant causal mechanism – i.e., long-term memory – that defines kind membership. The condition that Machery labels “Default” partially captures this idea.
In short, Machery's comments, appropriately construed, provide reason to suppose that concepts are a natural kind in the HPC sense.
Why would one think otherwise?
Clearly, Machery is not inclined to accept this conclusion. Why not? Here are some brief comments on the most plausible arguments that we could extract from his discussion.
Argument 1: Different kinds – for example, prototypes and theories – satisfy the conditions on concepthood. So, while prototypes and theories might be natural kinds, concepts as such are not.
Response: There is nothing wrong with superordinate natural kinds. For example, metal is plausibly a natural kind, even though it contains subordinate kinds such as gold and lead. For all the present argument shows, the same is true of concepts.
Argument 2: Characteristics 1–7 are intended to explicate the cognitive scientist's notion of a concept, not to characterize the kind as such. If so, treating them as parts of the kind-syndrome is tantamount to confusing issues about the semantics of the word “concept” with issues about the nature of the kind.
Response: Even if 1–7 are parts of the cognitive scientist's notion of a concept, there is no inconsistency between this claim and the claim that they are also parts of the property cluster exhibited by members of the kind.
Argument 3: Members of a natural kind are supposed to share many covarying properties and, hence, be subsumed by many empirical generalizations. But while concepts share some properties, and are subsumed by some empirical generalizations, there are too few to merit natural kind status.
Response: How many properties must members of a kind share in order for the kind to be natural? This is a silly question because there is no reason to suppose any precise cut-off point. Presumably some kinds manifest more common properties than concepts do, and, in that regard, are better examples of natural kindhood than concepts. But this is a very unsurprising conclusion. (Who would have supposed otherwise?) Moreover, it surely does not follow from this that concepts are not a natural kind simpliciter. On the contrary, there are two obvious considerations that explain the relative lack of properties and generalizations associated with concepts without impugning their natural kind status:
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1.
Concept is a psychological kind; and psychological kinds quite generally appear to underwrite fewer empirically rich generalizations than the kinds cited by many other disciplines. (Exercise: Compare chemistry or molecular biology with psychology.)
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2.
Concept is a superordinate kind. So, in point of logic, the kinds it subordinates –for example, prototypes and exemplars – will have the characteristics of concepts as such, plus their own specific characteristics. Still, it would be wrong to suppose that only subordinate kinds are natural, while kinds like concept (or metal, or alkali, etc.) are not.
Conclusion
Concepts plausibly constitute a natural kind, in the HPC sense. So, pace Machery, we do not advocate their elimination from cognitive science. Instead, we think that Machery's discussion supports a rather more banal conclusion, namely: Concepts are, in some regards, a less good example of natural kindhood than many other kinds studied by science. But this is very unsurprising, and is largely explained by two facts: Psychology appears to generate fewer robust empirical generalizations than many other sciences; and in point of logic, superordinate kinds manifest fewer regularities than the kinds they subordinate.
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Introduction
A central claim of Machery's Précis (target article) – and of his book, Doing without Concepts (Machery Reference Machery2009) – is that concepts do not constitute a natural kind. Until reading his work on the topic, we would have been inclined to agree. But he has changed our minds. Machery's discussion, when appropriately construed, provides grounds to suppose that concepts do constitute a natural kind.
What is a natural kind?
Though the notion of a natural kind has been characterized many times over, philosophers of science have, in recent years, reached a consensus – or as close to consensus as philosophers ever get – according to which natural kinds are Homeostatic Property Clusters (HPC; Boyd Reference Boyd1991; Machery Reference Machery2005). According to the HPC account, a kind K is natural if:
H1. It is associated with a contingent property cluster: a range of characteristics or symptoms which tend to be co-instantiated by instances of the kind, but need not be genuine necessary conditions for membership.
H2. There is some set of empirically discoverable causal mechanisms or structures – a causal essence – that explains the covariation of these symptoms.
H3. To the extent that there is any real definition of what it is for something to be a member of the kind, it is not the symptoms but the presence of the causal essence producing the symptoms that are definitive of kind membership (Boyd Reference Boyd1989).
This conception of natural kinds is intended to capture the central features of those kinds paradigmatically studied by science. Most importantly, the fact that the existence of property-clusters depends on the operation of an underlying causal essence helps explain why such kinds are typically subsumed by many non-accidental, empirical generalizations (Griffiths Reference Griffiths1997; Machery Reference Machery2005).
Why suppose that concepts constitute a natural kind?
Machery endorses the HPC account, yet he denies that concepts constitute a natural kind. We maintain, however, that if his claims about the cognitive scientist's notion of a concept are correct, then concepts are plausibly a natural kind in the HPC sense. First, consider some of the characteristics that, according to Machery, concepts possess:
1. Concepts consist in bodies of information.
2. Concepts are stored in long-term memory, and persist even when not actively deployed.
3. Concepts are non-proprietary.
4. Concepts are default representations automatically retrieved from long-term memory.
5. Concepts are subject to temporal and inter-subjective variation.
6. Concepts are internally connected.
7. Concepts are internally coherent.
No doubt other generalizations hold of concepts as such. But even the characteristics 1–7 just listed provide grounds to suppose that concepts are a natural kind. If true, they suggest that concepts satisfy the main conditions imposed by the HPC account. Specifically:
C1: Concepts exhibit a reliably covarying property cluster, including internal coherence, connectedness, persistence, and so on.
C2: The existence of the property cluster depends largely on the operation of an abstractly, functionally characterizable kind of process. Roughly: Most of the properties depend on facts about long-term memory, the operations that it performs, and its relations to other higher cognitive processes.
C3: To the extent that inclusion in the kind, concept, can be defined, it should be the condition of being subject (in the right kind of way) to the relevant causal mechanism – i.e., long-term memory – that defines kind membership. The condition that Machery labels “Default” partially captures this idea.
In short, Machery's comments, appropriately construed, provide reason to suppose that concepts are a natural kind in the HPC sense.
Why would one think otherwise?
Clearly, Machery is not inclined to accept this conclusion. Why not? Here are some brief comments on the most plausible arguments that we could extract from his discussion.
Argument 1: Different kinds – for example, prototypes and theories – satisfy the conditions on concepthood. So, while prototypes and theories might be natural kinds, concepts as such are not.
Response: There is nothing wrong with superordinate natural kinds. For example, metal is plausibly a natural kind, even though it contains subordinate kinds such as gold and lead. For all the present argument shows, the same is true of concepts.
Argument 2: Characteristics 1–7 are intended to explicate the cognitive scientist's notion of a concept, not to characterize the kind as such. If so, treating them as parts of the kind-syndrome is tantamount to confusing issues about the semantics of the word “concept” with issues about the nature of the kind.
Response: Even if 1–7 are parts of the cognitive scientist's notion of a concept, there is no inconsistency between this claim and the claim that they are also parts of the property cluster exhibited by members of the kind.
Argument 3: Members of a natural kind are supposed to share many covarying properties and, hence, be subsumed by many empirical generalizations. But while concepts share some properties, and are subsumed by some empirical generalizations, there are too few to merit natural kind status.
Response: How many properties must members of a kind share in order for the kind to be natural? This is a silly question because there is no reason to suppose any precise cut-off point. Presumably some kinds manifest more common properties than concepts do, and, in that regard, are better examples of natural kindhood than concepts. But this is a very unsurprising conclusion. (Who would have supposed otherwise?) Moreover, it surely does not follow from this that concepts are not a natural kind simpliciter. On the contrary, there are two obvious considerations that explain the relative lack of properties and generalizations associated with concepts without impugning their natural kind status:
1. Concept is a psychological kind; and psychological kinds quite generally appear to underwrite fewer empirically rich generalizations than the kinds cited by many other disciplines. (Exercise: Compare chemistry or molecular biology with psychology.)
2. Concept is a superordinate kind. So, in point of logic, the kinds it subordinates –for example, prototypes and exemplars – will have the characteristics of concepts as such, plus their own specific characteristics. Still, it would be wrong to suppose that only subordinate kinds are natural, while kinds like concept (or metal, or alkali, etc.) are not.
Conclusion
Concepts plausibly constitute a natural kind, in the HPC sense. So, pace Machery, we do not advocate their elimination from cognitive science. Instead, we think that Machery's discussion supports a rather more banal conclusion, namely: Concepts are, in some regards, a less good example of natural kindhood than many other kinds studied by science. But this is very unsurprising, and is largely explained by two facts: Psychology appears to generate fewer robust empirical generalizations than many other sciences; and in point of logic, superordinate kinds manifest fewer regularities than the kinds they subordinate.