There continues to be an impressive appetite for conceptual and philosophical explorations of psychiatry. The publishing field is now populated by a diverse array of backgrounds and perspectives. The general public seems mostly interested in decrying the medicalization of normal and the transformation of our woes into neatly packaged mental disorders. The academic literature is dominated by philosophers and philosophically-trained professionals; while the intellectual discourse is of high caliber, it unfortunately remains largely inaccessible to mental health professionals and much of the general public, and resultantly it has had little influence outside the academic community. There is also a cohort of individuals with a critical interest in the subject but whose philosophical focus remains stuck on classical critical figures such as Thomas Szasz, Michel Foucault and R.D. Laing, with little engagement with contemporary philosophy of science. The philosophical work of Kenneth Kendler and his various collaborators (John Campbell, Carl Craver, Kenneth Schaffner, Erik Engstrom, Rodrigo Munoz, George Murphy, and Peter Zachar) assembled in a specially curated volume occupies a unique and special position in this contemporary landscape and there is much to be said in its favor.          

Ken Kendler needs little introduction within psychiatry: he is an internationally renowned and highly respected psychiatrist and genetics researcher, who has been further catapulted into fame over the past two decades through his widely read philosophical commentaries. While the book is clearly focused on Kendler’s philosophical writings, majority of the articles in this collection have been written by Kendler in partnership with various co-authors; foremost among them is his long-term philosophical collaborator and friend Peter Zachar, who is also the co-editor of the book. These philosophical ideas are therefore the product not of a single mind but rather of multiple intellectual collaborations (Zachar is an intellectual heavyweight in his own right, as evidenced by his 2014 book A Metaphysics of Psychopathology).      

This book is a selection of 21 of Kendler and company’s most important philosophical and historical papers published over the course of his career. These articles are organized in the book into the following content areas: classification and the nature of mental disorders, mind and body, causality and explanation, psychiatric genetics and neuroscience, and historical studies. The book is not merely a rehashing of previously published material, however. There is a new foreword by Robert Freedman (psychiatrist and former editor of The American Journal of Psychiatry), and the book begins with a biography of his life and scholarly career (written by Peter Zachar) which offers us valuable insight into the man behind these articles. Most importantly, each article in the book is preceded by a new introduction by Kendler in which he explains the context in which the article was written, summarizes the conclusions, and reflects on how well the article has stood the test of time.   

The introductions are by far the most interesting portion of the book. Kendler writes these with a great degree of candor and personal touch. The introductions have the lively and dynamic quality that characterizes Kendler’s lectures and presentations. The contextual details provided in the introductions may seem minor, but they actually end up adding a lot more flavor and make the articles much more accessible. 

 

There are several aspects which make this book unique in the publishing world of philosophy and psychiatry. It is aimed primarily at medical and mental health professionals and is relevant to their conceptual concerns. Kendler writes first and foremost as a psychiatrist who is troubled by the instability of philosophical foundation of psychiatry and is trying his best to make sense of it. It is my experience as a psychiatrist and reader of philosophy of psychiatry literature that philosophers sometimes lack familiarity with psychiatric presentations in real-world settings, while having a good understanding of “textbook psychiatry”, of clinical syndromes as they are described in the diagnostic manuals, and this can impact the relevance of their conclusions. Kendler, in contrast, is not only a psychiatrist but a leader in the field. He has been involved with revisions of the Diagnostic and Statistical Manual of Mental Disorders (DSM) since DSM-III-R. He is intimately familiar with the workings and internal politics of DSM task force committees. As a geneticist and psychiatric researcher, he is well-versed in the latest neuroscience, and understands all too well what neuroscience can and cannot deliver for clinical psychiatry. Kendler is one of a kind among his psychiatric peers: I am hard-pressed to think of any other living psychiatrist who has the breadth of historical knowledge, rigor of scholarship, excellence in research, and depth of philosophical understanding that Kendler possess.

Kendler writes in a very clear language, with limited use of philosophical jargon, and ample use of clinical examples. He makes frequent illustrative comparisons of philosophical issues in psychiatry with philosophical issues in neuroscience, biology, and physics. However, in return he also expects a lot from the reader. Kendler extends an eager hand, but the reader is also expected to rise to the level of Kendler’s intellect. The reading is accessible, fertile, and extremely rewarding, but it is by no means “easy”. Kendler’s passion for the subject shines throughout the book. His intellectual rigor is apparent and impressive. Even when talking about philosophical and abstract issues, he is always grounding himself in empirical data. Almost every paper in this collection makes extensive references to empirical studies from psychiatry. The selection of articles is well done and the organization of the book does a good job in demonstrating the evolution of his thought over time.   

The contents of this 550-page book can be difficult to encapsulate in an essay of any length, however, I will attempt to summarize major recurrent themes from this collection. Readers can appreciate the inter-related nature of these ideas, and how they collectively function as a coherent whole of Kendler’s philosophical universe.

The role of non-empirical factors, social processes, and “value judgments” in psychiatric nosology: In the very first article Kendler points out how psychiatric nosology keeps “running into the limits of the scientific method”. For instance, there are multiple validators of psychiatric diagnosis (such as genetics, longitudinal course, treatment response, etc.) and these validators do not necessarily converge. Which validators to prioritize – in other words, what do we want psychiatric diagnoses to accomplish – cannot be answered by scientific evidence and has to be decided by pragmatic goals and value judgments. The role of social processes and value judgments is examined in greater detail in the last section when the history of the diagnostic status of homosexuality and premenstrual dysphoric disorder is discussed. Kendler acknowledges that he is greatly perturbed by the implications. However, he finds solace in the fact that psychiatry is not alone in facing this, and even “hard sciences” such as astronomy face similar challenges. 

Anti-reductionism and scientific pluralism: Kendler make his hostility towards “hard biological reductionism” very clear throughout the book. He writes, “I really want to drive nails into the coffin of hard biological reductionism. It has distorted our field, narrowed our thinking, and reduced the richness of the intellectual life of too many psychiatrists” (p 156). This antireductionism is reflected in his own research work in psychiatric genetics where he is strongly critical of attempts to find a “gene for” major psychiatric disorders. 

In lieu of reductionism, Kendler endorses “scientific pluralism”. There are multiple explanatory perspectives available to us to understand psychiatric disorders and one perspective cannot be reduced to another perspective (he shares a wonderful example from biology of how mechanistic biology and evolutionary theory offer equally valuable explanatory perspectives in explaining why the male peacock has such an elaborate tail). This pluralism can also be understood in terms of multiple “levels of explanations” such that one level cannot be reduced to another. Kendler characterizes his pluralism as “empirical” and “hard-nosed” by which he means: “risk factors have to earn their place at the table. Pluralism does not mean that “everything” needs to be considered in an etiologic model. Researchers advocating a particular level need to produce data of high quality with a focus on causal processes. Hand-waving is not enough nor are emotional pleas for inclusivity or for the “bio-psycho-social” model” (p 278).

Explanation-aided understanding and linking the brain to the mind: In one of the articles, Kendler shows us how Jasperian dichotomy between causal explanation and empathic understanding may not be as unbridgeable as Jasper had believed, and that certain neuroscientific explanations (such as abnormalities of dopamine driven salience system) can in fact facilitate our psychological understanding of psychiatric phenomena such as delusions. 

In line with this theme, he emphasizes at several places in the book that our work to uncover the causal mechanisms of psychiatric disorders is not done until we have traced the story from the basic biological processes back into the mind. “The work isn’t done until we can bring our etiological models back into the world of the mental and actually explain the often distressing symptoms that our patients are displaying” (p 279).

Dappled and complex nature of causality in psychiatry: Disorders for which it is easy to both identify the specific causal processes and to identify on what scientific level they exist are termed “monocausal” by Kendler. He argues with an impressive review of empirical literature that major psychiatric disorders are not monocausal. There are no single causes and the causal risk factors are spread out, or “dappled”, across multiple levels of explanation, from molecular genetic all the way up to cultural forces. The dappled and complex nature of causality in psychiatry has several important implications: First, “This requires us to give up the dream that the next great technology of science will show us that we really have monocausal disorders” (p 215). Second, this serves as a reminder that dualistic models and organic-functional dichotomies are a poor fit for psychiatry. “In no case do these distributions [of causal risk factors for major psychiatric disorders] resemble that predicted by the organic-functional/hardware-software dichotomy” (p 245). 

Interventionist model for causality: The interventionist model for causality de-emphasizes a priori metaphysical ideas about what causality is, and instead focuses on a “what if” question: how would the world differ if the intervention in question did versus did not occur, assuming other variables remain the same? This model attracts Kendler a great deal. It connects causation with practical interests of psychiatry, it “slices through” the mind-body problem, it separates the question of causation from the question of mechanisms, and importantly for Kendler, it enables empirical pluralism by allowing the study of causation across multiple levels of explanation. 

Epistemic iteration: Iteration originated as a computational method that generates a series of increasingly accurate estimations of a desired parameter. In an iterative system, each new estimate is an improvement over the previous estimate. This concept was expanded into the notion of ‘epistemic iteration’ and applied by Hasok Chang to the history of science of temperature, and Ken Kendler applies it to psychiatric nosology.

“If our current methods for validating psychiatric disorders, including description, genetics, imaging, treatment response and follow-up studies, reflect aspects of an objective truth out there in the world and we want our nosology to describe those truths with increasing accuracy, the only way to achieve this is to assure ourselves that each periodic revision of our manuals contains improvements on its predecessor. That is, changes are only made on the basis of convincing evidence that, using an agreed upon set of validators, the new diagnostic criteria improve upon the performance of their predecessor” (p 57).

Kendler realizes that psychiatric constructs are messy and there are too many non-empirical factors in play that epistemic iteration will never be as consistently progressive as the development of thermometers was, but he hopes for a “middle ground of wobbly iterations”.  

Metaphysical nature of psychiatric disorders: Kendler describes the three metaphysical positions of realism, pragmatism, and constructivism. Realism implies that psychiatric disorders are “real things” in the world that we can discover. Pragmatism states that psychiatric disorders are categories we propose because they are practically useful to us. Constructivism, as Kendler sees it, holds that psychiatric disorders are things cultures and individuals create not discover. While Kendler started his career as a strong realist, he now describes himself as sitting “somewhere between realism and pragmatism” with “an acceptance that constructivism plays a role and is something we need to keep an eye on” (p 82). Kendler has given up the idea that psychiatric disorders have a single essence. Instead he sees them as “networks of interacting causes and symptoms like Boyd’s homeostatic property clusters. The stability of our disorders over space and time is an emergent property of the human mind-brain system – not the result of one essence from which all the symptoms and signs develop” (p 97).

Diagnostic anti-literalism: Despite all the hard work Kendler has put into the development of DSM over his career, he worries that the DSM criteria are taken too seriously. He is particularly bothered by the unreflective attitude that the DSM criteria are pretty much all we need to know about psychiatric syndromes. “This attitude drove me a bit crazy as if the publication of the most recent DSM edition covered everything important in the rich and diverse clinical descriptive tradition of our field” (p 137). Kendler’s argument against diagnostic literalism lies in a distinction between indexical and constitutive criteria. DSM criteria are indexical when they serve merely as a fallible way of measuring or identifying a disorder. DSM criteria are constitutive when they truly and definitively define a disorder, i.e. having a disorder is nothing more than meeting the DSM criteria. Kendler’s discussion makes it very clear that DSM criteria are not constitutive, and that they capture only a subset of the clinical manifestation of a disorder.

Historically contingent nature of psychiatric nosology: Another recurrent theme in Kendler’s work is that psychiatric nosology sits in a historically contingent developmental arc. This is illustrated beautifully in the last section of the book on historical studies, particularly the results of Kendler’s scholarly efforts to understand the development of Kraepelin’s diagnostic concepts (he went so far as to partner with a translator to obtain translations of previously untranslated writings of Kraepelin from German to English!). Kendler passionately acknowledges, “Our approach to psychiatric disorders did not arise de novo along with DSM-III or its key predecessors. Rather, these efforts arose as part of a historical arc whose origins go back to Kraepelin and two of his key predecessors – Kahlbaum and Hecker” (p 474) and laments that the lack of historical knowledge has not served psychiatrists well in our current DSM debates. 

Kendler’s arguments are extremely persuasive. He makes them with such force and clarity, and marshalls so much empirical evidence in support that most readers would find it difficult to reject his arguments outright. When disputes cannot be settled by empirical evidence, reasonable people can disagree regarding what philosophical approach to take. The goal in such situations is not to produce arguments that would convince skeptics (philosophical arguments rarely, if ever, have such power) but rather to show that the philosophical approach one is advocating is metaphysically coherent and empirically informed, has pragmatic utility, and invites productive debate. Kendler does an excellent job on all counts. 

It is clear from Kendler’s biography as well as from some of the introductions that much of the intellectual labor behind the articles in this book may not have been possible without the extrⒸaordinary support he received from his wife Susan Miller. Like all life on earth, the act of living up to one’s full potential (what the Greeks called arete) requires not just the potential but also a habitat capable of supporting that development. It is too easy to forget that all great things are accomplished in an ecosystem. All of us who have benefitted from Kendler’s work, we owe a note of gratitude to his better half.

Until the “collected works of Kenneth Kendler” are published at some point in the future, and I’d wager that the publication of such an epitome is more likely than not, Toward a Philosophical Approach to Psychiatry is likely to remain the most comprehensive and authoritative introduction to the philosophical writings of Ken Kendler, and a must read for all interested in the subject of philosophy of psychiatry.

 

Ⓒ 2020 Awais Aftab

Awais Aftab, MD, is a psychiatrist in Cleveland, OH. He leads the interview series “Conversations in Critical Psychiatry” for Psychiatric Times. He is on twitter @awaisaftab.

Categories: Philosophical

Keywords: philosophy, psychiatry