I saw a discussion online in which one participant claimed that the atheist/naturalist has no way to objectively define what a mental illness is, since they have no objective way to ground how a brain ought to function in the first place. It is certainly an ongoing controversy in psychology to define what behaviors should be considered maladaptive or mental illnesses, and since psychology has a de facto assumption of methodological naturalism, is it impossible to objectively define what a “properly functioning brain” is? This is a slightly redacted version of my reply to that discussion. It is obviously only scratching the surface of the issue but they were my initial thoughts.
By what standard do we judge a brain to be “malfunctioning?” After all, there is Hume’s is-ought problem, since saying how a brain is seems to be a different kind of thing than saying how it ought to be. “Ought” implies a second set of value judgments to be applied to things that are. Secondly, if a “mental illness” improved an organism’s adaptiveness, and this illness is passed to future generations, is it really an illness?
Here’s a mild example: most people have systematic biases in their thinking but this is considered normal. For instance, if you ask a Psych 101 classroom full of students to rate themselves on how funny they think they are compared to the average person, the vast majority will rate themselves higher than average. But obviously this cannot be – if people were able to rate themselves objectively, half would be above the median and half below. So this is one example of a bias in our thinking that disconnects us from reality a bit, but the reason it exists is that it provided some evolutionary advantage. The same is true with self-ratings of loyalty, honesty, being a good driver, attractiveness, and a number of other social cognitions.
So to create a “just-so story” on the topic, we can consider that long ago there was a caveman who rated himself slightly funnier than average (though this was unjustified). However, this gave him a bit more social confidence which is adaptive and allowed him more social leverage and he was more likely to pass on his genes.
So whether this story is true to reality or not, it shows that a “healthy” brain is not necessarily a brain that most accurately perceives reality. Secondly, we can consider most measurable factors of brain functioning falling on a normal bell curve. Let’s take dopamine. If we assume for the sake of argument that too little dopamine results in problems (say, Parkinson’s disease) and too much dopamine results in problems (say, schizophrenia), we can expect that most people have average amounts of dopamine so it’s not a problem for them, but variation in reproduction results in some at the top and some at the bottom.
But this results in other variations too. Some people have a huge IQ and some have a small IQ. I would assume that a higher IQ is more adaptive than a lower IQ. However, we would not consider a higher IQ to be an “illness.” Just a slight deviation from the norm – one that ends up being adaptive.
So this means that a mental illness is not necessarily synonymous with:
1. A correct perception of reality (sometimes it’s better not to be in touch with reality).
2. A major deviation from the “norm” if we assume a normal distribution of any given mental factor (some deviations from the norm are adaptive, and in fact, every good adaptation we have was once a major deviation of a previous population, that increased adaptive fitness and was passed down to us).
That leaves adaptability. I think the atheist/naturalist can still define mental illness as any condition that makes a person less likely to pass on their genes to the next generation. Certainly severe schizophrenia makes it less likely that a person might pass on their genes (because they can’t hold down a steady job, can’t find a mate, experience social rejection, etc.). And, in fact, that is generally how psychologists define mental illness. There is quite a range of behaviors that would seem strange to most people but a psychologist might tolerate, unless that behavior interfered with a person’s life (job, intimate relationships, ability to feed themselves, etc.).
However, this brings up other issues. What if a person does not want to have children? Is this a “mental illness?” It certainly means that the person is less likely to pass on their genes to offspring. But do we really need to institutionalize people who don’t want kids?
Secondly, the factors that may make a person more likely to pass on genes is quite culture-specific. A person who has daily supernatural visions in poor areas of the Dominican Republic might be regarded as a spiritual or holy person, worthy of respect, while a person who has daily supernatural visions in wealthy New York City might be institutionalized by his/her family. Also, norms are fluid. The “normal” IQ of a paleolithic man (or a previous hominid IQ) would be different from the “normal” IQ of a modern man. We can consider that the “Unfrozen Caveman Lawyer” may have been the smartest caveman around, but in the modern era he still might be at a significant disadvantage.
As an A-T guy* it’s much easier for me to think that objects are naturally directed towards ends, and a “mental illness” is therefore any condition that prevents the brain from achieving its natural end. But there are issues with this approach, too (for instance, who decides what the natural end of a thing is? A brain with schizophrenia might be a perfectly functioning brain, if the end is to have schizophrenia). So the point is, I don’t think it’s impossible for an atheist/naturalist to come up with a definition of “mental illness” that is grounded in something more objective, though it’s not as easy as it seems up front, and there seem to be lots of issues with any definition of mental illness I can think of.
*or more accurately, a psychologist who is inclined toward A-T philosophical thinking.