In this post, Harriet Fagerberg and Justin Garson discuss their new paper, “Proper Functions are Proximal Functions,” forthcoming in The British Journal for Philosophy of Science (preprint here).
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| Harriet Fagerberg |
What makes something a mental disorder? Why are schizophrenia, bipolar disorder, and depression mental disorders, but not jealousy, grief, or racism? This is philosophy of medicine’s famous “demarcation problem.”
We think that what makes something a mental disorder, rather than an ordinary response to the problems of life, or run-of-the-mill social deviance, is that there’s a dysfunction. Something in the person’s brain isn’t working as designed. The same is true of the rest of medicine. What makes diabetes or leukemia diseases, rather than just unpleasant things to have (like being short), is that they involve dysfunctions.
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| Justin Garson |
But what are functions? By ‘function’ we just mean effects that were favored by natural selection. The function of the heart is to pump blood, rather than make beating sounds that you can hear through a stethoscope, because that’s why natural selection put it there. Part of the job of science is to identify the functions of the parts of our bodies and minds. Part of the job of medicine is to fix them when they go wrong.
In short, we think that diseases (or disorders) involve dysfunctions, and dysfunctions happen when something can’t do whatever evolution put it there to do. One benefit of this point of view is that it makes it an objective fact of the matter whether a trait is functioning correctly, and thus whether it is or isn’t diseased or disordered. But this simple and elegant picture has a serious problem. This is the “problem of function indeterminacy”. This is the problem we attempt to solve in our paper.
The function of any given trait, like the heart, is associated with a whole sequence of activities. Hearts pump (contract and expand). By doing that, they move blood around the body. By doing that, they bring oxygen to cells and get rid of waste products. And by doing that, they keep us alive. So, which one of those activities is the heart’s real function? Are all of those activities its functions? Or only one? And if so, which one?
One point of view is that our question is misguided. Any of those activities can be its “function,” depending on where your interests lie. A cardiologist might say that the function of the heart is to pump, because that’s what they are interested in. A pulmonologist might say the function of the heart is to bring oxygen to cells, because that’s what they care about.
We disagree with this view. That’s because, if function is relative to your goals and values, then dysfunction is relative to your goals and values, too. And that would defeat the whole point of introducing functions into conversations about disease and disorder. After all, if dysfunctions are relative to goals and values, then they cannot serve as an objective break on what is and isn’t a disease.
Fortunately, we think there is a principled answer to the question of which of the heart’s activities is its real function: a trait’s proper function is its most proximal function. It’s the very first activity in the sequence of activities. We think the function of the heart is just to pump. It’s not to move blood around. Nor is it to bring oxygen to cells. Those are functions of larger systems of which the heart is a part.
We have several reasons for thinking that proper functions are “proximal.” It explains some commonsense features of functions, such as the fact that different parts of the body have different functions. It also makes sense of our conventional practices of intervention, for example, doctors generally only intervene on the heart when it can’t perform its most proximal function. Finally, it preserves the attractive, naturalistic idea that diseases involve dysfunctions, and functions depend only on objective facts about the world, rather than our personal or collective value judgements.
The idea that proper functions are proximal might actually have interesting implications for how we think about mental illness. That’s because it suggests that sometimes, traits or conditions we think of as dysfunctional really aren’t – even if they appear strange or maladaptive at first glance.
Suppose Riad has Capgras delusion, and he thinks that his wife has been replaced by a perfect impostor. It’s easy to think that in this case, there must have been a terrible dysfunction within Riad’s “belief-forming” mechanism. But that depends on what, exactly, Riad’s belief-forming system is supposed to do.
If the function of the belief-forming system is to form true beliefs, then Capgras delusion would seem to involve a dysfunction. But if the function of the belief-forming system is to form beliefs that hang together with perceptual data, then it could be performing its function just fine.
Judgements about function and dysfunction aren’t just theoretical. They are practical. They guide our choices about whether and how to intervene. In Riad’s case, they might influence a doctor’s choice about whether to prescribe antipsychotic drugs that could have dangerous side effects. That’s why we think it’s so important to be precise and careful about how we describe something’s function.