ad hoc hypothesis

In science, an ad hoc hypothesis is an assumption made in response to facts that are inconsistent with a theory in order to prevent the theory from being falsified. By extension, an ad hoc hypothesis is any assumption made to save a claim from being refuted. What are often called ad hoc hypotheses might better be referred to simply as rationalizations.

One of the more important ways of testing a scientific theory is to deduce observations that should occur under specified conditions if the theory is correct. An experiment may create those conditions and if the predicted observations occur, the theory is said to be confirmed. Experiments that confirm a theory should be replicable. If the predicted observations do not occur and it is determined that the theory cannot be correct if they do not, then the theory is falsified. Likewise, if experiments fail to replicate confirmations and it is determined that the theory cannot be correct if replication doesn't occur, then the theory is said to be falsified. If a new fact is discovered that is inconsistent with the theory, the fact must be accommodated. The theory might be tweaked or it may be preserved by hypothesizing another fact that would make the first fact consistent with the theory. Or, the fact might prove the theory false.

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When William Hershel discovered the planet Uranus in 1781 by telescopic observation, it was also discovered that the new planet’s orbit was different from what it should have been according to Newton’s laws. The orbit of Uranus was an anomaly: a phenomenon that apparently did not fit with the Newtonian paradigm. Some scientists may have thrown up their hands and said: “See, Newton was wrong! Hah!” Others may have offered the ad hoc hypothesis that the anomalous orbit was caused directly by God. Uranus has a different kind of orbit than the other planets because God is working a miracle—suspending the laws of nature—perhaps to demonstrate his power and existence to us. But most scientists set to work to solve the puzzle. The simplest solution was to posit another planet beyond the orbit of Uranus whose gravitational force was affecting the planet’s orbit. This hypothesis could be independently tested. Its size and orbit could be calculated based on how much it perturbed the motion of Uranus. Thus was Neptune discovered. When the math for Neptune’s orbit didn’t work in accordance with Newton’s laws, it was proposed that still another planet awaited discovery. The object known as Pluto gave astronomers the data to show that Neptune did, after all, orbit in accordance with Newton’s laws. Both of these hypotheses could be independently tested, albeit with some difficulty given the state of knowledge and technology at the time.

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When Alfred Wegener proposed his theory of continental drift in 1912 against the prevailing theory that the Earth was formed by cooling from a molten state and contractions, 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,” wrote Stephen Jay Gould (Ever Since Darwin. W.W. Norton & Company.1979, p. 163).

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George Dillman claims that he and his top students can knock out people by manipulating some sort of subtle energy called qi (chi or ch'i, pronounced chee). When 8th degree black belt Leon Jay failed to move Luigi Garlaschelli with qi, Dillman offered the following ad hoc hypotheses. 1. Garlaschelli is a total non-believer and you must believe you can be knocked out by qi for the power to work. 2. Garlaschelli might have had one big toe pointing upward and the other pointing downward. If so, the power won't work. 3. Maybe Garlaschelli wasn’t knocked out because his tongue was "in the wrong position."

While Dillman's hypotheses seem like obvious rationalizations, they have the merit of being empirically testable to a degree. Qi remains undetectable by science's most refined measuring instruments, but we can at least test the toe and tongue position claims. If the no-touch knockout doesn't work even when the toes and tongues are aligned the way Dillman wants them, we'll at least know that these hypotheses are false. On the other hand, if Jay or Dillman knocked over Garlaschelli without touching him when his toe and tongue were aligned, we'd have evidence in favor of the qi hypothesis.

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Defenders of alleged psychic Edgar Cayce provided a classic rationalization to explain away their hero’s failures. For example, Cayce and a famous dowser named Henry Gross set out together to discover buried treasure along the seashore and found nothing. Their defenders suggested that their psychic powers were accurate because either there once was a buried treasure where they looked but it had been dug up earlier, or there would be a treasure buried there sometime in the future.

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Some scientists think they have evidence for the existence of ESP. They predict that in card-guessing experiments where there are five choices, guessing correctly 20% of the time is expected by random chance. Proponents of ESP maintain that if a person has psychic ability, she will select unseen cards correctly at a rate that is statistically significant, i.e., a rate not likely due to random chance.

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 the outcome. Of course, if this ad hoc hypothesis is taken seriously, then no experiment on ESP or PK (psychokinesis) can ever fail: Whatever the results, one can always say they were caused by paranormal psychic forces, either the ones being tested or the hostile ones not being tested. The "hostile energy" hypothesis can't be independently tested. (Some dowsers who fail tests of their art also appeal to the hostile energy of skeptics interfering with their powers. And some practitioners of facilitated communication who fail scientific tests of their ability are excused because the testing made them nervous and unable to get the communication from their clients.)

Psi-missing is an ad hoc hypothesis invented by parapsychologists to explain away failures to demonstrate ESP. The tests usually involve trying to use ESP to identify various targets, such as Zener cards, pictures, etc. which are hidden from direct view of the subject. The failure to do better than would be expected by chance is explained away as due to unconscious direction to avoid the target.

Psychic drift is the entry of unintended non-target data into the psychic transmission or reception path during a psi experiment. Psychic drift may account for some telepathic subjects guessing the wrong card, photo, video clip, etc. They're getting information inadvertently sent from a card game in Las Vegas, a psi experiment in Edinburgh, or a television program from an apartment in Moscow. Or, psychic drift could be another ad hoc hypothesis used by parapsychologists to explain away psi failure.

Physicist John Taylor explained that the reason the children he was studying for their psychokinetic powers could bend forks and spoons with their minds only when nobody was looking was because of "the shyness effect." The children weren't shy; paranormal phenomena are. Taylor hypothesized that paranormal phenomena have an aversion to scrutiny.

When a psychic dowser was unable to distinguish bottles of regular water from those he claimed he had energized with healing properties, he hypothesized that his magic water had energized all the bottles of water in the room. You can view this rationalization on Nova's "Secrets of the Psychics" with James Randi. The magic water hypothesis is reminiscent of the claim that several copies of the shroud of Turin exist because the original has the magic property of transferring its image to nearby cloths.

Ingo Swann, an advocate of remote viewing, claimed that he saw a 30,000 ft. mountain range on Jupiter on an astral voyage when there is no such thing. Swann, in a lovely ad hoc hypothesis, now claims that astral travel is so fast that he probably wasn't seeing Jupiter but another planet in another solar system! There really is a big mountain out there on some planet in some solar system in some galaxy.

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Dorothy Martin led a small UFO cult in the 1950s. She claimed to get messages through automatic writing from extraterrestrials known as The Guardians. Like the Heaven’s Gate cult forty years later, Martin and her followers—known as The Seekers or The Brotherhood of the Seven Rays—were waiting to be picked up by a spaceship. In Martin’s prophecy, her group of eleven would be saved just before the total destruction of Earth by a massive flood on December 21, 1954. When the day of reckoning came and went, it became evident that there would be no flood and that the Guardians were no-shows. Martin allegedly became euphoric. She claimed that she’d received a telepathic message from the aliens explaining that God had decided to spare the planet as a reward for their great faith. All but two of her merry little band failed to recognize that this new revelation was rationalized rubbish. They not only stuck with her despite the absurd improbability of her claim; their devotion actually increased. (Some believers in faith healing and intercessory prayer claim that failures are due to people not having enough faith.)

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Believers in biorhythms claim that our daily lives are significantly affected by rhythmic cycles overlooked by scientists who study biological rhythms. When confronted with cases that conflict with the predictions of biorhythms, defenders claim that some people are arrhythmic. Another favorite ad hoc hypothesis concerns the claim that biorhythms can predict with 95% accuracy the sex of an unborn fetus. When the prediction was wrong that was because the fetus was a homosexual and homosexual fetuses have indeterminate sex identities!

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One of my favorite ad hoc hypotheses comes from Philip Henry Gosse who argued in Creation (Omphalos): An Attempt to Untie the Geological Knot (1857) that God created the world a few thousand years ago complete with fossils. Another favorite comes from a defender of Nostradamus, who argued that Nostradamus predicted the Challenger space shuttle disaster on January 28, 1986. The allegedly predictive quatrain reads, in part, "From the human flock nine will be sent away." To account for the fact that there were only seven on board, it was posited that Christa McAuliffe was pregnant with twins.

Another example of providing a whopper of a rationalization involves Uri Geller. In 1973 Geller appeared on the Johnny Carson "Tonight Show" and was supposed to demonstrate his ability to bend spoons with his thoughts and identify hidden objects, but he failed to even try. He squirmed around and said something about how his power can't be turned on and off, and that he didn't feel strong right then. Actually, James Randi had worked with Carson's producer to change the spoons and metal items that Geller planned to use, as there was a suspicion that Geller likes to work (i.e., soften) his metals before his demonstrations, as would any careful conjurer.

Psychologist Ray Hyman provides the most dramatic example of rationalization that I've ever come across. A chiropractor hypothesized that randomized, double-blind, controlled tests of causal claims "don't work" rather than admit that his belief in applied kinesiology had been falsified by such a test.

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Offering alternative explanations for something is not the same as proposing an ad hoc hypothesis. If I say of someone who recovers from an illness after going to an energy healer that she might have recovered had she not consulted any healer and that the illness might have resolved itself on its own, I am not trying to save my hypothesis that energy healing is placebo medicine by offering an ad hoc hypothesis. Offering plausible alternatives is not the same as rationalizing to save a belief, especially when the plausible alternative has been demonstrated in many independent tests.