Nick Haslam (2002) Natural Kinds, Practical Kinds, and Psychiatric Categories. Psycoloquy: 13(001) Biological Psychiatry (2)

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PSYCOLOQUY (ISSN 1055-0143) is sponsored by the American Psychological Association (APA).
Psycoloquy 13(001): Natural Kinds, Practical Kinds, and Psychiatric Categories

Review of Zachar on Biological-Psychiatry

Nick Haslam
New School University
Department of Psychology
65 Fifth Avenue
New York, NY 10003


"Psychological concepts and biological psychiatry" presents a compelling critique of the biomedical materialist approach to mental disorder. This review focuses on its conceptualisation of disorders qua categories, particularly its rejection of the natural kind concept and its proposed concept of "practical kinds."


folk psychology, eliminativism, evolution, psychiatry, pragmatism, essentialism, biomedical model, philosophy of science, natural kinds
1. Zachar's book (2000) commences with a sharp critique of eliminative materialism and a sustained and many-pronged defence of folk psychological explanation. Rather than being a pre-scientific way to account for mind and behavior that will inevitable yield to neuroscience, he argues, folk psychology is fundamental to psychology as a whole. The claims of neuroscience to explanatory superiority are still in large part promissory, and motivated by a crude and over-zealous scientism. Zachar dubs this revolutionary eliminativist movement "anti-anthropomorphism". He goes on to defend an uneliminable basis for psychology by defining its domain as a level of analysis between internal and external worlds. This proposal, he argues, avoids many of the problems that result from a definition of psychology's field as mentalistic phenomena, and combats the unhelpful opposition of the psychological and the biological. Zachar goes on to propose several additional "anchors of psychology" that buttress the discipline's claims to value and scientific autonomy.

2. Zachar's broad critique of eliminativism leads into a critical evaluation of biomedical materialism as a foundation for the conceptualisation and treatment of mental disorders. This evaluation is spread over several closely argued and well exemplified chapters, and defends several propositions of real importance to the concerns of mental health researchers and clinicians. Justice cannot be done to these claims here, but they can be laid out to give a sense of the ground covered. First, despite being scanted by the biomedical approach, the phenomenal character of mental disorders is a crucial part of its formal classification and practical diagnosis. Subjective phenomena are not eliminable as sources of clinical evidence and are in many cases constitutive of particular disorders. Sensitive attention to the patient's subjectivity is correspondingly crucial for treatment. Second, in part because psychiatric classification rests on subjective phenomena (i.e., symptoms), it is wrong of some critics to dismiss classification as in some way anti-psychological, or as purely a component of the dreaded "medical model."

3. Other criticisms take issue with models of etiology and treatment. According to the third, the bottom-up explanation of mental disorders as products of specific genetic or physiological etiologies typically fails in view of the causal complexity of most disorders. Fourth, such "broken brain" accounts are also insufficient because they neglect evolutionary, adaptive or functional considerations. These require a distinctly psychological analysis because they cannot be captured by internal neural states but only in the organism-environment interactions that constitute the psychological domain, by Zachar's account. Fifth, given the inadequacy of causal accounts that invoke specific biological abnormalities, it is inappropriate for psychiatric treatments to target the brain exclusively. Instead, a therapeutic pluralism is required, and psychological treatments can be embraced without abandoning a materialist stance towards disorder. Finally, Zachar challenges biological psychiatry's claim to ease the social suffering of the mentally disordered by reducing stigma and neglect. He argues convincingly that there are no unambiguous grounds for seeing the biomedical position as uniquely humanitarian.

4. All of these criticisms of biomedical approaches to mental disorder have been made before in some form (for recent examples see Haslam, 2000; Kiesler, 1999; Luhrmann, 2000; Valenstein, 1998) but rarely if ever have they been mustered with this book's level of philosophical sophistication, breadth of attention, and balance. Readers will find in this book an unusually comprehensive yet balanced critique.

5. One topic on which I have some disagreements with Zachar is his discussion of the misunderstanding of mental disorders as natural kinds. This understanding is arguably a core feature of the biomedical approach to psychiatry. It holds that mental disorders are disease entities that are categorically or qualitatively distinct from normality, grounded in discrete biological causes, and that they exist independent of social construction and the changing conventions of psychiatric diagnosis. This implicit understanding of psychiatric diagnoses is indeed widely held among biomedically-oriented psychiatrists. It drives a reductionist research agenda that seeks localized pathologies, a treatment agenda that over-emphasizes pharmaceutical palliation, and a complacency about the transferability of categorical diagnosis from general medicine into psychiatry. The view of mental disorders as natural kinds is therefore a deserving and vitally important target for a critique such as Zachar's.

6. Zachar rebuts this natural kind view of mental disorder because the essentialism it implies is implausible. He argues that disorders cannot be classically defined, cannot be accounted for by inhering properties alone, and have multiple intersecting causes, all of which conflicts with an essentialist formulation. Moreover, the existence of a static essence makes little sense from an evolutionary or functional perspective. This critique of essentialist thinking about mental disorders is important not only for its relevance to the professional discourse of biomedical psychiatry, but also because essentialism pervades laypeople's thinking about mental disorder (e.g., Haslam, 2000; Haslam & Ernst, in press; Haslam, Rothschild & Ernst, 2000).

7. One problem with Zachar's analysis is that he identifies natural kinds with essentialist categories. Although there is ample precedent for this equation (e.g., Kripke), it is arguably possible to separate essentialism from the natural kind concept (Haslam, 1998). Boyd (1984), for instance, has proposed an understanding of natural kinds as homeostatic property clusters that possess coherence and crisp boundaries but lack necessary features. Most biological kinds are probably well understood in this fashion. It is well known that species cannot, after Darwin, be seen in an essentialist manner, as they lack necessary features, maintain their boundaries dynamically and relationally, change over time, and occasionally show gradations between species. However, they remain natural kinds in any meaningful sense of the term.

8. When we ask whether a mental disorder is well understood as a natural kind, I would argue, we are asking not whether it has an essence but whether it has a comparable ontological status to naturally existing biological kinds. That is, we are asking whether it has relatively crisp boundaries, is objectively real rather than merely reflecting classificatory conventions, and has a biological basis. Are mental disorders akin to biological species, with an equally solid, non- artifactual foundation in the natural world? In many or most cases, the answer will be a clear "no". However, the answer is obviously and uninterestingly "no" if we require a natural kind to have an essentialist basis that is implausible even for biological species. Almost no-one doubts that "carving nature at the joints" -- even if it is an ugly metaphor -- is a reasonable and feasible goal when it comes to biological taxonomy at the species level, even if these joints are not defined by essences. The question ought to be whether we can have the same confidence in the existence of "natural" joints and objective discontinuities in the psychiatric domain. In short, I think Zachar deflects the real challenge of the natural kind view of mental disorders by joining it to the important but distinct issue of essentialism.

9. A second problem with Zachar's analysis of mental disorders is that his preferred alternative understanding of disorder, once the natural kind view has been abandoned, is left quite unspecified. Zachar coins the term "practical kind" to refer to a form of category that is neither essentialist nor arbitrary or artificial. What precisely qualifies a kind as being "practical" is unfortunately left rather unclear in the book. As best as this reader can tell, a practical kind is a way of carving the psychopathological domain that makes no pretense of seeking objective "joints" but rather strives for divisions that are indistinct and context-relative but useful in some respect. Utility might be understood as informativeness for clinical judgement i.e., affording many inferences about the characteristics of members of the kind, such as their developmental history, comorbid conditions, and prognosis or perhaps more narrowly as treatability. A practical kind might be one whose members typically respond positively to a particular form of intervention, so identifying them as belonging to such-and-such a kind is pragmatically valuable.

10. The trouble with the practical kind concept is not that it is incoherent or an inappropriate basis for psychiatric classification. Rather, the concept rules out the possibility that there are some mental disorders that are non-arbitrary categories -- marked off from normality and from other disorders by an objective boundary or discontinuity -- but are not grounded in essences. That is, there are mental disorders that are not natural kinds in an essentialist sense but that have a firmer objective basis than the concept of "practical kind" admits. To recognize only practical kinds in the psychopathological domain is to commit oneself to the position that truly discrete and non- arbitrary kinds do not inhabit the domain, and that it is instead intrinsically continuous, graded, or "fuzzy." This also amounts to a reaction against the default assumption of biomedical psychiatrists that disorders are crisp essentialist categories; it is an equally unempirical assumption that discrete categories do not occur. This is a common assumption among psychologists, one often held as an article of disciplinary faith, and it leaves them prone to dismiss or suspect categorical diagnostic systems such as DSM-IV (although Zachar is quite balanced about its merits). It also leaves them likely to be found wrong in regard to particular disorders.

11. Perhaps the best way to illustrate this point is through research that uses Paul Meehl's "taxometric" methods (e.g., Meehl, 1995). These methods make no a priori assumptions about whether latent variables are best construed as discrete, bounded categories or as continua, but tests rigorously between these alternatives. The practical kind concept implies that there are no non-arbitrary discontinuities in psychopathology, only dimensions and gradients on which divisions are to be placed according to pragmatic considerations. The natural kind concept, in contrast, implies that discontinuities are legion and possibly grounded in essences, and that it is the job of a classification system is to carve up psychopathology at these discontinuities. Taxometric methods search for discontinuities, seek multiple convergent sources of evidence for any discontinuity that is found, and estimate parameters of the categories found in this manner (e.g., their prevalence). Zachar is appropriately skeptical of attempts to resolve psychiatric classification by statistical means, but taxometrics is considerably more robust than earlier methods. Moreover, unlike these methods it does not prejudge the issue by inevitably imposing a categorical or continuous structure on the domain it maps (cf. cluster analysis and factor analysis, respectively). In short, taxometrics offer a way to test whether discrete categories, based on objective discontinuities rather than pragmatic decisions, exist in the psychopathological domain, contrary to the practical kind concept.

12. The empirical research to date is illuminating on this question. To this point there have been more than forty taxometric studies of more than twenty psychopathological variables (see Haslam & Kim, 2001, for a review). A modest majority of studies have favored "taxonic" (i.e., categorical) solutions, finding evidence of a bounded latent category corresponding more or less well to a DSM-IV disorder or to one of its proposed subtypes. (A somewhat smaller number of studies of normal personality variables has also been conducted, and a small but noteworthy minority of these also appear to be taxonic.) The point here is that discrete categories based on discoverable discontinuities rather than pragmatic divisions appear to be widespread, but far from universal as a strong form of the biomedical view would claim. Mental disorders are apt to be heterogeneous in nature -- some categorical entities, some pragmatic divisions imposed on graded continua and deciding between these alternatives in a particular case should be an empirical matter. To rule out the existence of discrete categories on account of a commitment to anti- essentialism is to make a significant but well-motivated mistake.

13. One reason this ruling-out constitutes a mistake is the widespread distribution of non-arbitrary categories in psychopathology, which leads to a misidentification of objective discontinuities as pragmatic divisions. Another reason is that it is not at all difficult to develop models of mental disorder that are consistent with the existence of objective discontinuities but do not invoke essences. Of course, a discrete psychopathological kind might arise out of an essence-like cause such as a genetic abnormality (e.g., Down's syndrome) or germ (e.g., general paresis). However, other non-essentialist models are also possible, for example developmental polarization, non-linear interactions of vulnerability factors (e.g., emergenesis), and threshold effects. In most cases of apparently discrete mental disorders, complex multifactorial causal models such as these are far more plausible than essentialist models. In addition, there is no reason to expect that when a form of psychopathology is found to be discrete the relevant causal factors will tend to be biomedical in character. Thus, believing in the existence of bounded psychiatric entities entails no commitment to essentialist explanation. Zachar's endorsement of practical kinds as an anti-essentialist classification strategy therefore seems to this reader to retreat too far from the natural kind concept. We need a classificatory concept intermediate between practical kind and natural kind.

14. This said, Zachar's proposal must also be applauded in two respects. First, the role of pragmatic considerations in psychiatric classification is often neglected by taxonomists, some of whom persist in a blind faith that psychiatric taxonomy is exclusively a matter of carving nature at the joints. The practical kind concept is a useful remedy to this dogma. Second, some mental disorders almost certainly are best described as practical kinds rather than discrete categories. One important example is major depression, which taxometric research (e.g., Ruscio & Ruscio, 200) finds to fall on a severity continuum with everyday sadness and misery, with no qualitative discontinuity. Clinicians require a practical distinction to be made all the same, and the DSM-IV appropriately obliges. The same is true in general medicine: essential hypertension and obesity appear to reflect extremes on continua, but recognizing both as practical kinds is vitally important for diagnosis and treatment.

15. I have focused my criticisms on one rather small part of what is an ambitious and important contribution to the literature in its field. This book has many appealing qualities. As a critique of biomedical approaches to psychopathology it is unusually thorough and free of the polemic and diatribe that distort many writings. Zachar acknowledges the successes of biomedical formulations and treatments and the virtues of psychiatric classification, but retains a clear-eyed recognition of their limitations and the epistemic hubris of some of their more aggressive proponents. He does an unusually solid job of conducting serious philosophical work and making it relevant and comprehensible to the psychological reader. It is to be hoped that the book is read and heeded. It will raise and sharpen the debate if it is.


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Haslam, N., & Ernst, D. (in press). Essentialist beliefs about mental disorders. Journal of Social and Clinical Psychology.

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