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David Duff had some thoughtful comments on my post about Stephen Jay Gould's arguments in The Mismeasure of Man about whether IQ is a "real thing" or just the result of measurement. I will provide further illustration of what I meant in that post, and then share some thoughts from a biography of Einstein that speak to David's last sentence. ("This is not reification, this is normal science.")
To show that creating a numeric index does not necessitate an underlying reality, suppose I created a "health-per-wealth" index to determine whether someone ate sufficiently healthy for a member of their social class. To create my index, we count the number of different types of vegetables in someone's refrigerator and divide that by the number of walls in their home. My own number right now is an embarrassingly low 0.16. Now, has this measurement told me anything about how healthy I am relative to other members of the population? Not really. Nor would adding more data on other individuals help to do so. The measure itself is flawed, relying on two (very) imperfect proxies for real underlying characteristics. Most people would agree that health and wealth are real concept, but we learn very little about them from shopping habits and architecture. Likewise, intelligence seems to me a real enough "thing," but I am not convinced that IQ tests are an accurate measure, nor that any one-dimensional measure would suffice.
Speaking more directly to David's point about whether reification inheres in normal science, I would concede that it does. This is the essence of inductive or causal reasoning: to take disparate facts and reason that there is some logic underlying them, and hopefully a relatively simple logic at that. But we cannot be convinced that it actually exists without a great deal of either experimentation or faith, or both. Walter Isaacson's excellent Einstein has a helpful example from the debate between Einstein and Planck over quantum theory:
For Planck, a reluctant revolutionary, the quantum was a mathematical contrivance that explained how energy was emitted and absorbed when it interacted with matter. But he did not see that it related to a physical reality that was inherent in the nature of light and the electromagnetic field itself....
Einstein, on the other hand, considered the light quantum to be a feature of reality: a perplexing, pesky, mysterious, and sometimes maddening quirk of the cosmos. For him, these quanta of energy (which in 1926 were named photons) existed even when light was moving through a vacuum. (p. 99)
At stake here is exactly the same issue as in the IQ case--whether a theoretical concept (in this case, quanta) was a feature of reality or a mere incident of measurement. Modern physical theory has generally accepted the reality of quanta, but the acceptance was by no means automatic.
Isaacson's book makes clear how the scientific process can be affected by personal politics. Later on, Einstein takes Planck's side in a debate over relativity and the principle of least action.
Planck was pleased. "As long as the proponents of the principle of relativity constitute such a modest little band as is now the case," he replied to Einstein, "it is doubly important that they agree among themselves." (p. 141)
In another instance, Isaacson describes how increasing anti-Semitism spurred Einstein into being more conscience of his Jewish identity. (Some might ascribe this to a social form of Newton's third law.) The biography is interesting throughout, and highly recommended.