Do Extraordinary Claims Need Extraordinary Evidence?

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Exposing the skeptics linguistic sleight of hand.

You can’t travel far on the internet without hearing someone chanting the mantra: Extraordinary claims require extraordinary evidence. It’s often assumed that merely reciting the incantation is sufficient to reject any idea its power is aimed at.

The saying was popularized in Carl Sagan’s 1979 book Broca’s Brain in reference to paranormal claims, but it’s since become a catch cry for skeptics everywhere to instantly dismiss any idea they find unbelievable.

Its rhetorical power has even taken hold in more respectable scientific contexts. It’s been called “a fundamental principle of scientific skepticism” and claimed to be “at the heart of the scientific method, and a model for critical thinking, rational thought and skepticism everywhere.

If the slogan is a fundamental maxim of skepticism, it’s an embarrassment to have so many self-proclaimed skeptics failing to question their own maxim.

What makes a claim extraordinary?

What type of evidence is extraordinary?

Tracing the origin of the slogan

To answer these questions, we can trace the origin of the phrase to the philosopher David Hume’s essay, Of Miracles (1748), which is part of his classic work, An Inquiry Concerning Human Understanding.

In his essay Hume gives us an accurate description of what extraordinary means. Hume thinks evidence is derived from our experience of the world, and the laws of nature are established based on repetitions of those experiences.

Hume argued that a miracle requires extraordinary proof or evidence because by definition, a miracle was “a violation of the laws of nature” and those laws of nature were established by countless experiences of them happening.

To believe a miracle has occurred was “a contest of two opposite experiences”. To witness a miracle is to have a single experience of the laws of nature being violated, but against this experience we have the many experiences that caused us to consider it a law of nature.

Hume gave as one example of a miracle, a piece of lead held in the air which remains suspended when released. If we’ve observed a thousand times that lead will fall to the ground when dropped, to believe a miracle has occurred requires a thousand and one observations of it remaining suspended in the air.

Whatever you think about the success of Hume’s empirical argument, his intention about the meaning of extraordinary is clear. Extraordinary means large amounts of evidence. For a claim to be extraordinary means it already has large amounts of evidence to the contrary.

There isn’t some different type of evidence we need, or some different type of claim we’re assessing, extraordinary refers to the quantity of evidence we already have. An extraordinary claim is one for which we already have an extraordinarily large amount of evidence it is false.

Exposing the sleight of hand

The sleight of hand is to call the claim extraordinary, when extraordinary really refers to the evidence. There aren’t different types of claims, there are different amounts of evidence for claims. Sometimes we have a lot of background evidence for a claim so we can easily say if it’s true or false. Sometimes we don’t have much evidence for a claim, and we might withhold judgement on its truth and remain agnostic.

But despite this quantitative or probabilistic meaning of extraordinary we see Sagan’s slogan used to dismiss anything someone personally finds unbelievable.

It’s often used to reject anything that sounds like pseudoscience because it’s a claim for which we currently have no scientific evidence. But far from being a skeptical maxim, this is a dangerous slide toward dogmatism.

There’s a crucial difference between phenomena which are outside the laws of nature and those which are outside current scientific understanding. Einstein once called quantum entanglement spooky action at a distance. The Big Bang was a term used to mock what is now a well-established scientific theory.

More importantly, focusing on phenomena that aren’t well understood is how scientific progress is made. As Thomas Kuhn said in his classic work, The Structure of Scientific Revolutions, “discovery commences with the awareness of anomaly”.

Which makes it even more regrettable that under the pretense of open-minded inquiry this skeptical slogan is often used to reject ideas which are disagreeable to materialistic beliefs.

The invisible assumptions

There is often the hidden suggestion that all natural claims are ordinary and reasonable, and all non-scientific claims are extraordinary and shouldn’t be believed. But this is only a colorful way of speaking. It gives the illusion naturalism is ordinary and reasonable and opposing views are extraordinary and unbelievable.

The skeptic may find the claims personally unbelievable, but personal incredulity has never been a good reason to reject a claim. A well-worn insult in philosophical circles is to denigrate a rationally hollow response as consisting only of an “incredulous stare”.

Once we expose the rhetorical trick, we find there are only plain old claims, the plain old evidence we have for those claims, and the mundane and laborious work involved to assess their truth.

Rather than being a maxim of skepticism, to say some claims are extraordinary misleads people how to think critically. It gives the impression some claims are given different treatment than others, whereas it’s really the evidence we should focus on.

The substance of the slogan reduces to the saying: Claims require sufficient evidence. But that is so trivially banal it’s unlikely to get much attention or generate the excitement needed to sell pop-science books.

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