Extraordinary Claims and Extraordinary Evidence

Are paranormal claims too 'extraordinary' for science?

IMAGE: Nightcafe

Just imagine that you’re sipping coffee watching the TV in the kitchen one morning when a friend comes in and says:

“There’s a pigeon on the roof again.”

My guess is that you wouldn’t bother rising from your chair. In the UK, pigeons are very common, so one on the roof is not surprising.

Now imagine that the same friend enters with a surprised look on their face.

“Did you know that there’s an elephant standing on your roof?”

My guess is that you’d be significantly more likely to dash outside, probably with your smartphone in hand for a photo. In the former case, you were willing to take your friend’s word that a pigeon was on the roof. The latter case is significantly unusual, and you’d like proof. (Assessing the damage to roof tiles might also be relevant).

This, in essence, is the logic behind the often-stated principle that “extraordinary evidence requires extraordinary proof”. If someone’s making an ordinary claim, then the level of evidence required is typically significantly lower than if someone is making an extraordinary claim. This is true in more than hypothetical cases. If someone claims to have witnessed a road collision, then all things being equal, you’re likely to take them at their word. If someone claims to have witnessed a ghost or a UFO, it’s likely that you’ll want to see the evidence.

Extraordinary Evidence?

IMAGE: Matt Colborn.

The phrase “extraordinary claims require extraordinary evidence” is often attributed to the astronomer Carl Sagan, but it didn’t originate with him.¹ It was first used by the sociologist Marcello Truzzi in 1975.² In a later article, Truzzi tried to clarify the meaning of the statement.³ A basic problem with paranormal claims, he thought, was the degree of evidence needed to establish whether a claim is true. This is often unclear because advocates and critics might differ significantly on the strength of evidence needed, say, to establish something like telepathy or precognition:

“Thus, on the one hand we may have the claimant offering evidence that is insubstantial for the critic, and on the other hand we may have a critic giving insubstantial indication of what it would take to force the critic to accept the evidence”. ⁴

So despite aspirations to objectivity, there’s a subjective element to scientific judgment. This complicates things. Outsiders to paranormal debates are often not only having to judge evidence, they’re also having to judge conflicting expert opinions on the implications of the evidence.

In the article, Truzzi also noted that that ‘extraordinary’ was always going to be a relative term. In the context of science:

“The question of extraordinariness….is relative to one's frame of reference, and when we are concerned with extraordinariness in a scientific context…such extraordinariness must be measured against theoretical expectations provided by the general body of scientific knowledge at the time”.⁵

In other words, a new claim is always going to be judged by what people already know — or think they know — about how the world works. Scientists in particular will judge ‘extraordinary’ claims against current knowledge. So a claim of telepathy might be perceived as unlikely because it seems to conflict with what a scientist thinks is well established about perception and brain function. This stance is inherently conservative, and often sensible. However, it can also be wrong.

Beyond science, people often judge claims based on common knowledge, as in the pigeon versus the elephant. In the UK, a pigeon on the roof is part of the accepted background of life. An elephant on the roof is not. This context will determine our reaction to the ‘extraordinary event’ of an (alleged) elephant on the roof.

The difficult question, as Truzzi stated, is what level of evidence is needed to establish the reality of an extraordinary event. To return to the elephant: just suppose that you leap out of the door and at first see nothing. However, your friend has taken a photograph showing the animal on your roof tiles. They insist that it’s not an AI fake, and it does not look obviously hoaxed. However, you understandably remain suspicious.

You decide to mount your own investigation, fetch a ladder from the garage and examine the roof for evidence. A tile or two is indeed damaged. There’s a dusty smudge that might be a footprint. And you find a cannon-ball shaped dropping.

This is the situation faced by investigators of paranormal and ‘fortean’ phenomena all the time. Very often, an ‘extraordinary claim’ or observation is accompanied by various kinds of circumstantial and trace evidence. For the most part, the evidence is suggestive, but insufficient to offer definitive proof.

The question is how strong evidence needs to be before you start taking the claim seriously. And as stated this is a subjective question, with subtleties. So, for example, there are different degrees of ‘extraordinary’. Truzzi pointed out that paranormal claims are not all equally unlikely in the light of current scientific knowledge and assumptions:

“Simple telepathy would not necessarily radically change our view of physics even if it caused major reconceptualizations in psychology and physiology. But the existence of clairvoyance and/or precognition would have quite revolutionary effects upon fundamental ideas in physics and almost all of science in so far as it might force alteration of our ideas about space and time. Yet both the proponents and critics of such claims commonly fail to consider the degrees of extraordinariness involved in the different anomalies discussed….”⁶

What this means is that, if we accept the principle, the evidence needed for telepathy need not be as strong as the evidence for clairvoyance (seeing at a distance) or precognition (seeing the future). This sort of nuance is often lost in debates over the paranormal, as Truzzi noted.

However, it can be usefully applied. The late visionary SF author Arthur C. Clarke did this in his TV show World of Strange Powers. In this, he gave different paranormal phenomena ratings in terms of their scientific plausibility. He rated ‘voodoo death’, apparitions and stigmata as “highly probable”; poltergeists and telepathy as “possible, worth investigating,” precognition as “barely possible” and was undecided about psychokinesis. He rated reincarnation and survival of death as “almost certainly untrue”.⁷ You might have your own judgments about these individual kinds of phenomena.

Extraordinary Claims critiqued

A 2016 paper by David Deming also critiqued the “extraordinary claims” principle. He claimed that it was false to separate evidence into two arbitrary categories – ‘ordinary’ and ‘extraordinary’. He suggested that “Science does not contemplate two types of evidence”. He also suggested that the “extraordinary claims” principle should not be used to “suppress innovation and maintain orthodoxy”.⁸

Demming:

“The confusion regarding what is meant by an “extraordinary claim” arises in simple carelessness. Carl Sagan did not define the term “extraordinary.” This allowed others to arbitrarily characterize as “extraordinary” any idea or claim that violated majority opinion”.⁹

So unfortunately, the “extraordinary claims” principle ended up bolstering aggressive public campaigns to write off paranormal claims without any serious thought. And if Deming is right then the problems with the principle mean that it’s less useful in a paranormal context than it might at first appear.

Now, about that elephant….

References

1. Sagan, C. (1979). Broca’s Brain. Random House.

2. Truzzi, M. (1975). Letter to the editor. Parapsychology Review, 6, 24–25.

3. Truzzi,  M. (1978). On the Extraordinary: An Attempt At Clarification. Zetetic Scholar, 1, p. 11-22. https://rr0.org/time/1/9/7/8/Truzzi_OnTheExtraordinaryAnAttemptAtClarification/index.html

4. Truzzi, 1978.

5. Truzzi, 1978.

6. Truzzi, 1978.

7. Clarke, A.C. (1985). Epilogue to Fairley, J. & Welfare, S. Arthur C. Clarke’s World of Strange Powers. Guild Publishing, p. 243.

8. Deming, D. (2016). Do Extraordinary Claims Require Extraordinary Evidence? Philosophia, 44(4), 1319–1331. https://doi.org/10.1007/s11406-016-9779-7

9. Deming, 2016.