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[THINKING ABOUT SCIENCE MASSIMO PIGLIUCCI Massimo Pigliucci is professor of philosophy at the City university of new york–lehman College, a fellow of the american association for the advance ment of science, and author of Nonsense on Stilts: How to Tell Science from Bunk. his essays can be found at www.rationallyspeaking.org.
What’s So Bad about Ad Hoc Hypotheses?
d hoc hypotheses are a staple of should sound almost as preposterous as leplin’s analysis of the issue of ad skeptical criticism of pseudo- the idea that skeptics weaken paranor- hocness, coming to the somewhat star- a science. i once participated in an mal powers below detectability, but the tling conclusion that the history of sci- experiment (well, really, a demonstra- so-called FitzGerald-lorentz contrac- ence suggests two major generalizations tion) about dowsing, during which we tion was advanced by established scien- about ad hoc hypotheses: first, an indi- showed that the alleged dowsing pow- tists and was eventually incorporated into vidual scientist’s judgment of a given ers of our subject were not, in fact, ca- our understanding of special relativity hypothesis as ad hoc (or not) is largely pable of finding water in randomized (though still not as an explanation of the based on a subjective evaluation and in- covered buckets any better than was lack of evidence for ether). What gives? formed by aesthetic criteria; second, the predicted by chance. the funny (to us Hunt provides several other examples judgment of the scientific community of ad hoc hypotheses entertained by the skeptics) thing was that the dowser had at large about a given hypothesis often tested his “powers” that day by checking scientific community (my favorite being changes retroactively, depending on that his dowsing rod was in fact work- Dennis Sciama’s “continuous creation” whether that hypothesis has been of ac- ing—when he could see whether there hypothesis in support of the steady state tual value in the scientific process or was or wasn’t water in the buckets. model of the universe and against the Faced with his abysmal failure during rival Big Bang theory). Hunt uses these not—something that is often impossi- the actual test, the dowser in question examples to debunk the notion—popular ble to assess at the moment when the used an old trumping card of the pseu- among philosophers and skeptics alike— hypothesis is first proposed. doscientist: it was the presence of skep- that ad hoc hypotheses are invariably bad Hunt then goes a step further to tics that had interfered with his powers. and easy to spot as such, contra what karl suggest that the very concept of ad hoc- Since it is hard to imagine a credible popper (he of the idea of falsificationism, ness ought to be abandoned on the test of paranormality that doesn’t in- see this column’s “philosophy of Science ground that it doesn’t do any useful volve the presence of skeptics, the “hy- 101,” Si, May/June 2004) famously work, perhaps to be replaced by notions pothesis” is as ad hoc (literally, “to this maintained. such as “warranted” and “unwarranted.” [specific purpose]”) as they come. For instance, Hunt examines the i don’t think the latter solution is any But now consider this quite different popperian idea that one crucial way to better than the problem it is supposed example. in 1887, A.A. Michelson and distinguish good from ad hoc hypothe- to solve, and i also think Hunt goes too e.W. Morley carried out a famous ex- ses is that the latter, but not the former, far in attempting to throw the whole idea periment to test the idea of the existence make predictions about genuinely new of ad hocness out the window. Just be- of ether, a mysterious substance that was phenomena. But the evidence from the cause there is an element of subjectivity thought to pervade space and allow light history of science clearly shows that sci- in science (is anyone really surprised by to propagate in it. the experiment failed, entists actually give a lot of weight to that?)—and even a role played by non- paving the way for the rejection of the retrodictions, i.e., to novel explanations empirical standards like aesthetics (again, notion of ether in physics, and it was of already known phenomena, if they surprising?)—doesn’t mean that there are eventually reinterpreted as a major con- appear to be fruitful within the cur- no differences between my dowser’s re- firmation of ein stein’s theory of special rently accepted paradigm of a given sponse to the failure of our little experi- relativity. And yet, as Christopher Hunt field of research. ment and the FitzGerald-lorentz con- points out in his brilliant recent paper on Another giant of philosophy of sci- traction. the real lesson for scientists, ad hocness (Philosophy of Science, January ence, Carl Gustav Hempel, suggested 2012), “George FitzGerald (in 1889) that perhaps what distinguishes an ad philosophers, and skeptics alike is that and Hendrik lorentz (in 1895) inde- hoc hypothesis from a genuinely scien- scientific theorizing is a complex activity pendently suggested another explana- tific one is that the latter makes “inter- that is not just the result of the applica- tion [of the Michelson-Morley negative estingly different” predictions, as op posed tion of strictly epistemic rules. Subjectiv- re sult]: the length of the arm of the to trivial ones. But as Hunt immediately ity, extra-empirical criteria, and even his- equipment parallel to the ether wind points out, this makes the whole thing torically evolving standards are in volved. shrank, because of an electrical effect pretty darn subjective: one scientist’s “in- Science (and skepticism) is a human ac- caused by the ether, by exactly the right teresting” prediction is another scientist’s tivity, done in the usual human, messy, amount to produce a null result.” to the trivial one (or vice versa). not at all air-tightly logical way. But it ear of the contemporary scientist this What then? Hunt endorses Jarrett seems to work, most of the time. n
18 Volume 36 Issue 5 | Skeptical Inquirer