Map of life expectancy at birth from Global Education Project.

Friday, August 25, 2006

The reification of constructs

We have been rathah amused by the frenzied flapdoodle over the de-planetification of Pluto. The journalistic profession and much of the public seem to think that this is a major scientific controversy and represents some substantive question about the nature of the universe.

Actually, it's the equivalent of a spat about what to name the baby. There is essentially no disagreement among astronomers about the nature of Pluto and the other objects known as planets. You can continue to call Pluto a planet if you want to, and the police won't knock on your door, nor will you be guilty of believing anything that isn't true. You will be using the word "planet" in a way which a scientific organization no longer chooses to use it, but what the heck, if I ask most people if a tomato is a fruit, they'll say no. The only real issue the Pluto controversy is convenience. Pluto turns out to be one of a very large class of objects orbiting the sun at a great distance. If we continue to call Pluto a planet, and we keep finding more of those objects, we'll end up with who knows how many planets, and it would be too hard to remember all their names. (Not that anybody would be obliged to do so.) That's the only issue at stake here.

A few days back I warned against confusing "is" and "ought" questions, a mistake which underlies many a ridiculous feud. Failure to recognize when an argument is purely semantic is probably an even more common cause of unnecessary strife. Unforuntately, it's also a cause of many substantive mistakes.

Take the "disease" called depression. Depression is defined clinically as whether or not a clinician decides, based on a conversation with a person, that some subset of a list of qualitative judgments about the person is applicable -- examples include fatigue, feelings of guilt, etc. For purposes of research, depression is normally defined as the score on a specific questionnaire called the Hamilton Rating Scale. One way to score points on the Hamilton scale is to deny being depressed.

Is there a "real" entity behind these definitions? In one sense, that's tautological. The entity is just that: how you answer those questions. However, psychiatrists want to be seen as "scientific" in their judgments and treatments, and drug companies want their pills to be seen as scientific treatments. Therefore they must believe that depression is something more than how people answer a series of stupid questions, that it corresponds to some biological process that can be independently observed. This compulsion has resulted in a widespread myth, that depression is a deficiency in the neurotransmitter serotonin. That hypothesis has been convincingly refuted, but as often happens (see my recent post on "two kinds of people"), the falsification has failed to "take," so strong is the need for depression to be "really real."

There is a common facile response to Popperian falsificationism. (Popperian falsificationism, Popperian falsificationism, Popperian falsificationism. I just wanted to say that.) Supposedly, if I say, "All swans are white," and you go out and find a black swan, I'll just say, "You call that a swan?" But that is too facile, I'm afraid, and utterly wrong.

If I have defined a swan as a white bird, then indeed, there cannot be a black swan, and the proposal is trivial. But that is not how biologists define species. It used to be. Taxonomists had only gross physical appearance to go on, so they could more or less arbitrarily decide that black panthers or white tigers were a different species. But now we define swans as birds which are interfertile with swans and are known to breed with other swans in nature. So, if a black one comes along who does that, not all swans are white, QED.

The point is, our thinking is constrained by how we sort things into categories. We can do that in a way which has a more or less compelling basis. These categories are constructs of the human mind, often strongly shaped by social pressures as well. That is what we mean by the social construction of reality. Reality is really real, but we humans need to put all the pieces into a finite number of buckets in order to make sense of it, and there are infinitely many ways of doing that. They are not, however, all equally defensible or useful.

The kinds of "fertile" research programs Imre Lakatos sees as definitive of science depend on fertile constructs. Whether we call Pluto a planet is trivial, it has no fundamental importance to astronomical research. But whether we call a score of 20 or more on the Hamilton Rating Scale the "disease" of depression is fundamental to how we address the problem of human happiness. That matters a lot.

No comments: