Article summary of The nature of psychiatric disorders by Kendler - Chapter

Realism is a theory in the philosophy of science. In this theory it is assumed that the content of science is real regardless of human perceptions and activities, which is also called “mind-independent”. There are two kinds (two flavors) of realism: one is based on the hard science of chemistry and the other biology. In hard science, elements in the periodic table are “mind-independent”.  An argument is, if other species would develop far enough, they would find something like our periodic table. The elements in this table also show another important point of realism, namely that of essences. When you know the atomic number of something, you can predict many other things about it. An essence is a metaphor for a “level” (the atomic number of elements). When you know something on a given level,  this tells you a lot about the other things.

In biology, biological species are most important. Species differ in four ways: their boundaries are less clear-cut, while the borders of elements are much sharper. Secondly, the conditions for existence are more conditional than for elements. Thirdly, species have no essence, while elements do: there is not just one thing that defines a whale. Finally, not all members of a species are identical to each other, while atoms in elements are. The biological flavor of realism is more appropriate to use to understand psychiatric disorders. Psychiatric disorders are more like species than like elements.

In pragmatism, key concepts in science are seen as ‘instruments’ or tools with which we can understand the world. In this view, scientific categories are judged on their usefulness and not on whether they are real or not. But pragmatism does not say anything about the underlying reality of psychiatric disorders.

Constructivism is a very anti-psychiatric perspective. Constructivism is about how people themselves construct things. This is also true for psychiatric disorders. An example of constructed psychiatric disorders are “iatrogenic disorders” which are disorders that patients have that are “constructed” from the expectations of therapists.

What are the two arguments against realism for psychiatric disorders?

Realism is considered to be the more useful option to understand the nature of psychiatric disorders. But there are two strong arguments against realism called: pessimistic induction (‘all past beliefs about nature have sooner or later turned out to be false) and historical contingency. Historical contingency means two things: when thinking about going back in history and re-writing the DSM and doing this a hundred times (called re-running the “tape of time”) it would not lead to reliable (consistent) psychiatric disorders. Secondly, our current diagnostic system seems to be dependent on historical events.  

Which four modifications exist for more useful realism?

There are four ways to modify the realistic perspective to be more useful for understanding psychiatric disorders

Homeostatic property clusters: These clusters tell that each psychiatric disorder has a unique set of causal interactions regarding symptoms, signs and underlying pathophysiology. This is a “softer” way than looking for true “essences”. It also has implications for how to understand the relationship between symptoms: it would be better to assume direct causal relationships between symptoms than to assume that each symptom is a reflection of an essence.

A more limited view of realism: Philosophy has two theories about when something is true: the correspondence theory (when someone says “It is raining” and this is happening, then this corresponds) and the coherence theory (considers something to be true when it fits with all the other things we know about the world).

Types of psychiatric disorders versus tokens: Tokens are part of a broader class which are called types. For example: Type (psychiatric disorders), sub type (mood disorder) and token (major depression). In psychiatry it would be better to focus on types instead of tokens, because this would lead to less pessimistic induction or historical contingency arguments.

A historical perspective applied to psychiatric disorders: This means that as long as disorders continue to provide us with new insights, they become more real. An example is that of “splitting” a diagnosis which leads to differences in treatment and etiology, which is called progressive diagnostic splitting. An example of this is Kraepelin’s splitting of the manic-depressive syndrome into major depression and bipolar illness.