Borsboom et al. have done an important service in drawing our attention to a problematic ideology espoused by some of psychiatry's most influential voices. In one sense the slogan “mental disorders are brain disorders” is unprovocative, since there are few Cartesians around anymore to defend the existence of “pure” mental substance. But the slogan is usually understood to declare something more radical: that mental disorders are to be explained in purely physical (or biological) terms. There is a rhetorical sleight of hand here, from a claim about constitution to a claim about explanation. The twenty-first century penchant for physicalism over dualism is being manipulated to fuel public support for a set of research strategies that the authors group under the banner of “explanatory reductionism.” Borsboom et al. aim to show that if, as they believe, mental disorders are best understood as causal networks of symptoms, then explanatory reductionism must be misguided.
In the philosophical literature, reductive explanations have traditionally been understood as explaining entities at a higher hierarchical level in terms of the interaction of constituent lower-level entities (Kaiser Reference Kaiser2015; Kauffman Reference Kauffman1971; Sarkar Reference Sarkar1992). Such explanations can be partial – what Schaffner (Reference Schaffner2006; Reference Schaffner2016) calls “patchy” – allowing reductionist methods to provide “creeping” but “not sweeping” accounts of the relevant phenomena. Borsboom et al. repeatedly acknowledge the value of such patchy reductions for psychiatry (e.g., see sections 4 and 7 in the target article). Nonetheless, they claim that these successes do not vindicate the reductionist program, because “they have not been translated into convincing reductive explanations of mental disorders through central pathogenic pathways rooted in neurobiology, as many had expected” (sect. 1, para. 3).
This representation of the explanatory reductionist as insisting “that it is possible in principle to identify a common pathogenic pathway at the level of the brain” (sect. 2, para. 7) is narrower than the philosophical use of the term, and is, in 2018, a bit of a straw man. Certainly there was optimism throughout the twentieth century that the biological essences of psychiatric disorders would be uncovered, to transformative effect. But the consensus now is that conditions such as schizophrenia and depression are profoundly polygenic, and are not caused by single biological abnormalities (Kapur et al. Reference Kapur, Phillips and Insel2012; Kendler Reference Kendler2013). Indeed, the leadership of the National Institute of Mental Health (NIMH), whom the authors rightly target as exemplifying explanatory reductionism, has emphasized that psychiatric disorders lack this sort of essential structure (Tabb Reference Tabb2015). Contrary to being motivated by the search for a common pathogenic pathway, as Borsboom et al. suggest (sect. 2), precision medicine's hunt for biomarkers aims to re-stratify the patient population in order to deal with the multiple realizability of diagnostic categories at the genetic and neuroscientific levels.
The relevant foil for patchy reductionism, then, is not a naive explanatory reductionism that assumes a simple causal story, but rather a triumphalist explanatory reductionism (hereafter, triumphalism) that maintains that the basic sciences will, in the end, provide all-purpose answers. When the authors argue that “mental disorders cannot be explained in terms of neural mechanisms” (sect. 1, para. 5), I take them to mean that triumphalism is misguided, because mental disorders cannot be entirely explained in terms of neural mechanisms. Reading the claim as a rejection of reductionism generally would put it at odds with the authors’ other statements about the value of patchy neuroscientific reductions. In any event, it seems that this sort of triumphalist overreach, rather than a focus on common pathways, makes the “mental disorders are brain disorders” slogan so frustrating, and its effects so pernicious.
For advocates of symptom network models, the costs of painting all reductionists with the same dismissive brush are relatively low. After all, their models concern non-hierarchical causal relationships, so they need not engage with reductionism of any stripe. Borsboom et al.’s conditional framing (see their Note 4 in the target article) represents just this kind of reasoning: If the network model is correct, then explanatory reductionism can and should be rejected. But their argument also allows for another conditional: If there exist other sorts of psychiatric causes besides symptoms which do act as underlying mechanisms, which do not include intentional features, and which are not socially constructed, then these features will remain ripe for reductive treatment. In other words, if one thinks that network relations do not provide the full causal story, one only has reason to reject sweeping reductions on the grounds the authors give, but can still pursue creeping ones.
The authors conclude by advocating for holism, “the research strategy that is focused on the interaction between parts rather than on their individual realization” (sect. 8, para. 6). Given this, they might allow the claim that mental disorders are in some sense brain disorders too, or in part, insofar as there is room for patchy reductive explanations even once the triumphalist ideology has been rejected. There is, however, another way to see symptom networks as only part of the causal story; not in terms of holism, but in terms of pluralism. The pluralist would take the models represented in Borsboom et al.’s Figure 1 more seriously than the authors do, assuming a heterogeneity of mental disorders in which some cases might be best understood at lower levels (Figs. 1a and 1b), some at higher levels (Fig. 2), and some at multiple levels (Figs. 1c and 1d). In contrast with the holist's, this conclusion is more modest; the pluralist only can be sure that not all mental disorders are exclusively brain disorders. But this is enough to logically entail a rejection of triumphalism. And it leads to a generative question the holist won't pursue: Which psychiatric cases admit of reductionist approaches, and which don't? Borsboom et al. provide the beginnings of this sort of rubric when they provide three circumstances under which mental phenomena will resist reductive explanation – but there is much more work to be done.
Just as valuable as the authors’ analysis of the canny sloganeering of the triumphalist is their own insurrectionist response. Their positive program might be captured by the alternative motto of “Symptomatology first!” As the authors importantly note, “to know which physical processes to investigate […], one needs to see these processes for what they are: as physical phenomena that might help us understand the bigger picture of symptoms and symptom networks in which we are ultimately interested” (sect. 7, para. 8). Basic sciences such as genetics and neuroscience will be of use for psychiatry only if they provide medical, rather than merely scientific, explanations. In this sense, Borsboom et al. are absolutely right to insist that we will always need psychopathology before reduction.
Borsboom et al. have done an important service in drawing our attention to a problematic ideology espoused by some of psychiatry's most influential voices. In one sense the slogan “mental disorders are brain disorders” is unprovocative, since there are few Cartesians around anymore to defend the existence of “pure” mental substance. But the slogan is usually understood to declare something more radical: that mental disorders are to be explained in purely physical (or biological) terms. There is a rhetorical sleight of hand here, from a claim about constitution to a claim about explanation. The twenty-first century penchant for physicalism over dualism is being manipulated to fuel public support for a set of research strategies that the authors group under the banner of “explanatory reductionism.” Borsboom et al. aim to show that if, as they believe, mental disorders are best understood as causal networks of symptoms, then explanatory reductionism must be misguided.
In the philosophical literature, reductive explanations have traditionally been understood as explaining entities at a higher hierarchical level in terms of the interaction of constituent lower-level entities (Kaiser Reference Kaiser2015; Kauffman Reference Kauffman1971; Sarkar Reference Sarkar1992). Such explanations can be partial – what Schaffner (Reference Schaffner2006; Reference Schaffner2016) calls “patchy” – allowing reductionist methods to provide “creeping” but “not sweeping” accounts of the relevant phenomena. Borsboom et al. repeatedly acknowledge the value of such patchy reductions for psychiatry (e.g., see sections 4 and 7 in the target article). Nonetheless, they claim that these successes do not vindicate the reductionist program, because “they have not been translated into convincing reductive explanations of mental disorders through central pathogenic pathways rooted in neurobiology, as many had expected” (sect. 1, para. 3).
This representation of the explanatory reductionist as insisting “that it is possible in principle to identify a common pathogenic pathway at the level of the brain” (sect. 2, para. 7) is narrower than the philosophical use of the term, and is, in 2018, a bit of a straw man. Certainly there was optimism throughout the twentieth century that the biological essences of psychiatric disorders would be uncovered, to transformative effect. But the consensus now is that conditions such as schizophrenia and depression are profoundly polygenic, and are not caused by single biological abnormalities (Kapur et al. Reference Kapur, Phillips and Insel2012; Kendler Reference Kendler2013). Indeed, the leadership of the National Institute of Mental Health (NIMH), whom the authors rightly target as exemplifying explanatory reductionism, has emphasized that psychiatric disorders lack this sort of essential structure (Tabb Reference Tabb2015). Contrary to being motivated by the search for a common pathogenic pathway, as Borsboom et al. suggest (sect. 2), precision medicine's hunt for biomarkers aims to re-stratify the patient population in order to deal with the multiple realizability of diagnostic categories at the genetic and neuroscientific levels.
The relevant foil for patchy reductionism, then, is not a naive explanatory reductionism that assumes a simple causal story, but rather a triumphalist explanatory reductionism (hereafter, triumphalism) that maintains that the basic sciences will, in the end, provide all-purpose answers. When the authors argue that “mental disorders cannot be explained in terms of neural mechanisms” (sect. 1, para. 5), I take them to mean that triumphalism is misguided, because mental disorders cannot be entirely explained in terms of neural mechanisms. Reading the claim as a rejection of reductionism generally would put it at odds with the authors’ other statements about the value of patchy neuroscientific reductions. In any event, it seems that this sort of triumphalist overreach, rather than a focus on common pathways, makes the “mental disorders are brain disorders” slogan so frustrating, and its effects so pernicious.
For advocates of symptom network models, the costs of painting all reductionists with the same dismissive brush are relatively low. After all, their models concern non-hierarchical causal relationships, so they need not engage with reductionism of any stripe. Borsboom et al.’s conditional framing (see their Note 4 in the target article) represents just this kind of reasoning: If the network model is correct, then explanatory reductionism can and should be rejected. But their argument also allows for another conditional: If there exist other sorts of psychiatric causes besides symptoms which do act as underlying mechanisms, which do not include intentional features, and which are not socially constructed, then these features will remain ripe for reductive treatment. In other words, if one thinks that network relations do not provide the full causal story, one only has reason to reject sweeping reductions on the grounds the authors give, but can still pursue creeping ones.
The authors conclude by advocating for holism, “the research strategy that is focused on the interaction between parts rather than on their individual realization” (sect. 8, para. 6). Given this, they might allow the claim that mental disorders are in some sense brain disorders too, or in part, insofar as there is room for patchy reductive explanations even once the triumphalist ideology has been rejected. There is, however, another way to see symptom networks as only part of the causal story; not in terms of holism, but in terms of pluralism. The pluralist would take the models represented in Borsboom et al.’s Figure 1 more seriously than the authors do, assuming a heterogeneity of mental disorders in which some cases might be best understood at lower levels (Figs. 1a and 1b), some at higher levels (Fig. 2), and some at multiple levels (Figs. 1c and 1d). In contrast with the holist's, this conclusion is more modest; the pluralist only can be sure that not all mental disorders are exclusively brain disorders. But this is enough to logically entail a rejection of triumphalism. And it leads to a generative question the holist won't pursue: Which psychiatric cases admit of reductionist approaches, and which don't? Borsboom et al. provide the beginnings of this sort of rubric when they provide three circumstances under which mental phenomena will resist reductive explanation – but there is much more work to be done.
Just as valuable as the authors’ analysis of the canny sloganeering of the triumphalist is their own insurrectionist response. Their positive program might be captured by the alternative motto of “Symptomatology first!” As the authors importantly note, “to know which physical processes to investigate […], one needs to see these processes for what they are: as physical phenomena that might help us understand the bigger picture of symptoms and symptom networks in which we are ultimately interested” (sect. 7, para. 8). Basic sciences such as genetics and neuroscience will be of use for psychiatry only if they provide medical, rather than merely scientific, explanations. In this sense, Borsboom et al. are absolutely right to insist that we will always need psychopathology before reduction.