When we were writing our book, it occurred to us that there was a kind of misinterpretation of which a very incautious reader might be guilty, and which we ought to do our very best to block. We did do our very best; but to no avail. Ned Block and Philip Kitcher make precisely the mistake that we’d dreaded. Worse, they then proceed to commit several other misreadings, the possibility of which, we admit, had not occurred to us. We’ll now do our very best to correct their mistakes, but time and space are pressing, and the opportunities for misinterpretation are, it appears, boundless.
First misreading: Block and Kitcher think we argue, erroneously, that “with respect to correlated traits in organisms—traits that come packaged together—there is no fact of the matter about which of the correlated traits causes increased reproductive success.” They then speculate that we are making “the very ambitious claim that whenever there are correlated traits there is no fact of the matter about which of the traits causes any effect.”
But, of course, we don’t believe, still less endorse, either of these theses. In fact, we think both are preposterous. We therefore spent our whole seventh chapter discussing a number of ways in which the causal roles of confounded variables can be, and routinely are, successfully distinguished. There are many such, the most obvious of which is perhaps John Stuart Mill’s “method of differences.” In effect, you run an experiment in which one but not the other of the correlated variables is suppressed. If you still get the effect, then it must be the variable you didn’t suppress that’s doing the causing. (If you think it’s maybe the ice rather than the alcohol that makes you tipsy, try taking one or other out, drink what’s left, and see what happens). People, scientists very definitely included, do this sort of experiment all the time. And often it works fine; we report lots of cases in our book. All this is familiar from Philosophy 101; do Block and Kitcher really believe that, old and case-hardened as we are, we could have failed to notice this?