An hypothesis created to account for a specific case or situation, especially a case which seems to refute one's theory, The ad hoc hypothesis tries to explain away apparently contradictory or falsifying evidence. For example, rather than admit that an experiment could not be duplicated because the esp it was supposed to confirm couldn't be confirmed, experimenters have been known to blame the hostile thoughts of onlookers for unconsciously influencing pointer readings on sensitive instruments. Of course, if this objection is taken seriously, then no experiment on esp or pk can ever fail: whatever the results, one can always say they were caused by paranormal psychic forces, either the ones being tested or others not being tested. This kind of ad hoc hypothesizing reached a ludicrous peak with paraphysicist Helmut Schmidt. He put cockroaches in a box where they could give themselves electric shocks. One would assume that cockroaches don't like to be shocked and would give themselves shocks at a chance rate or less (if cockroaches can learn from experience). The cockroaches gave themselves more electric shocks than predicted by chance. Schmidt concluded that "because he hated cockroaches, maybe it was his pk that influenced the randomizer!" [note 1]
Another type of ad hoc hypothesis is used when events occur which cannot be logically deduced from the original theory. In such cases, an ad hoc hypothesis is developed in an attempt to save the theory from being refuted. For example, if it occasionally rains on Fridays but you have offered a new theory of weather prediction from which we cannot logically infer that it will rain on any possible Friday, you might offer as an ad hoc hypothesis the claim that what we call Friday isn't really Friday but Thursday or Saturday looked at from the past or the future or from some other sort of calendar!
Ad hoc hypotheses are not limited to pseudoscientists. Another type of ad hoc hypothesis occurs in science when a new scientific theory is proposed which conflicts with an established theory and which lacks an essential explanatory mechanism. An ad hoc hypothesis is proposed to explain what the new theory can't explain. For example, when Wegener proposed his theory of continental drift he could not explain how continents move. It was suggested that gravity was the force behind the movement of continents, though there was no scientific evidence for this notion. In fact, scientists could and did show that gravity was too weak a force to account for the movement of continents. Alexis du Toit, a defender of Wegener's theory, argued for radioactive melting of the ocean floor at continental borders as the mechanism by which continents might move. "This ad hoc hypothesis added no increment of plausibility to Wegener's speculation." [note 2]
Ad hoc hypotheses are common in defense of biorhythm theory. For example, in finding that numbers of people do not fit the predicted patterns of biorhythm theory, the advocate either creates new rhythms to fit the data or claims that some people are arhythmic some or all of the time. Also, advocates of biorhythm theory claimed that the theory could be used to accurately predict the sex of unborn children. However, W.S. Bainbridge, a professor of sociology at the University of Washington, did a study which concluded that using the biorhythm theory the chances of predicting the sex of an unborn child were 50/50, the same as flipping a coin. An expert in biorhythms tried unsuccessfully to predict accurately the sexes of the children in Bainbridge's study based on Bainbridge's data. The expert's wife suggested to Bainbridge an interesting ad hoc hypothesis, viz., that the cases where the theory was wrong probably included many homosexuals with indeterminate sex identities!
Astrologers are often fond of using statistical data and analysis to impress us with the scientific nature of astrology. Of course, a scientific analysis of the statistical data doesn't always pan out for the astrologer. In those cases, the astrologer can make the data fit the astrological paradigm by the ad hoc hypothesis that those who don't fit the mold have other, unknown influences that counteract the influence of the dominant planets.
reader's comments
20 Sep 1996
As a skeptic I was delighted to find your dictionary on the net. Just as
I was about to conclude that the net is full of useless crap. (I'm a
neophite and I persevere. Obviously there is a great deal of useful
information and entertainment here.)
I think I understand that you are often playing the devil's advocate.
Some of the items you debunk do not necessarily deserve the offhand
dismissal you tend to dish out. Chiropratic for example does seem to
have some validity, but not the all pervasiveness that some exponents
would argue.
Anyhow, re your article on ad hoc hypothesis: When you, for example,
posit that in cases of hands on healing, chiropractic etc. that the
subject may have improved without any intervention at all, are you not
indulging yourself in a little ad hoc hypothesis? Perhaps this is called
fighting fire with fire.
I suppose this only points out how difficult it is to counter assumptions
that start from a premise that cannot be tested empirically.
Doug Harper
reply:Well, let's say I thought I caught you stealing a watch from a shop. You say you didn't steal it. I ask you to empty your pockets. You agree and pull out a watch. I say, "Aha, I was right. You stole the watch." You reply that you did not steal the watch, but you admit that it was not in your pocket when we went into the store. I ask you to explain how the watch got in your pocket and you say that you used telekinesis: you used your thoughts to transport the watch out of a glass case into your pocket. I ask you to repeat the act with another watch and you say "ok." But try as you will, you can't make a watch magically appear in your pocket. You say that there is too much pressure on you to perform and there are too many bad vibes in the air for you to work your powers. You've offered an ad hoc hypothesis to explain away what looks like a good refutation of your hypothesis. I have not offered an ad hoc hypothesis about anything. I don't call this fighting fire with fire, but fighting the implausible with the probable.