Carl Sagan

Sagan Standard: Extraordinary Claims Require Extraordinary Evidence

Carl Sagan once said, “Extraordinary claims require extraordinary evidence”, which is now known as the “Sagan Standard”. This means that if someone says something really surprising or unusual, they should have strong proof to back it up. It’s like telling a big story-you need to show it’s true. This idea is important today because there’s a lot of misinformation and conspiracy theories out there. So, Sagan’s rule reminds us to always ask for evidence before believing something that seems too amazing or out of the ordinary. If you’re going to make a big claim, you better have the facts to support it.

The Sagan Standard Explained

Carl Sagan used the phrase “Extraordinary claims require extraordinary evidence” in his 1979 book Broca’s Brain, which was named in honor of the French physician, anatomist, and anthropologist Paul Broca (1824-1880), and later in Cosmos, a thirteen-part, 1980 television series written by Carl Sagan, Ann Druyan, and Steven Soter.

This principle echoes the foundational tenets of scientific skepticism, and actually, it is at the core of the scientific method.

In many ways, Sagan’s Standard mirrors Occam’s razor. Both suggest that simpler explanations are often better than complex ones. However, the line between “ordinary” and “extraordinary” evidence isn’t always clear-cut. Over the years, the Sagan Standard has been a tool to question and critique both scientific data and pseudoscientific statements.

Historical figures like Thomas Jefferson (1743-1826, the third president of the United States from 1801 to 1809) in 1808 and the French scholar and polymath Pierre-Simon Laplace (1749-1827) in 1814 hinted at similar ideas.

Interestingly, almost the same phrase, “An extraordinary claim requires extraordinary proof,” was used by Marcello Truzzi (1935-2003), a professor of sociology, a scientific skeptic, and an investigator of various pseudosciences, just before Sagan popularized it. Truzzi’s remark is derived from aplace’s “plus un fait est extraordinaire, plus il a besoin d’être appuyé de fortes preuves” (the more extraordinary a fact is, the more it needs to be supported by strong evidence).

Some scholars even argue that a professor of sociology set the stage for the Sagan standard with his 1748 essay “Of Miracles.”

Later, the American writer and scientist Isaac Asimov also said something similar to the Sagan standard:

I believe in evidence. I believe in observation, measurement, and reasoning, confirmed by independent observers. I’ll believe anything, no matter how wild and ridiculous, if there is evidence for it. The wilder and more ridiculous something is, however, the firmer and more solid the evidence will have to be.

Isaac Asimov – quote from “The Roving Mind” (1983), Prometheus Books, new edition 1997. It is a collection of essays on creationism, pseudoscience, censorship, population, philosophy of science, transportation, computers, and corporations of the future, and astronomy.
Isaac Asimov also said something similar to the Sagan standard
Isaac Asimov also said something similar to the Sagan standard

Implementing the Sagan Standard

It is widely considered that the Sagan Standard is vital to the scientific method and a beacon for rational thinking. It’s often brought up when evaluating claims related to the paranormal or other pseudosciences. This principle gets invoked in scientific discourse, for instance, when assessing the validity of a newly identified species or when analyzing results funded by vested interests.

Its essence aligns with Occam’s razor. Essentially, an extraordinary claim should be the simplest explanation only when backed by equally extraordinary evidence. This, obviously, rarely occurs in pseudoscience or in conspiracy theories.

For example, conspiracy theories often rely on the belief that vast numbers of people can flawlessly coordinate and hide truths from the public. However, the plausibility of such scenarios becomes questionable when evaluated against human nature and practical logistics. So, it’s obvious that a conspiracy theory most probably isn’t the simplest explanation for a given phenomenon.

What is “extraordinary evidence”?

The main challenge, as Carl Sagan pointed out, is defining what “extraordinary evidence” really means. It can mean a significant volume of evidence rather than just high-quality evidence.

At first glance, “extraordinary evidence” may suggest evidence that is impeccably strong or of exceptionally high quality. However, it can also mean an abundance or significant volume of evidence that consistently points in the same direction. A single piece of compelling data might not be enough; instead, a convergence of multiple lines of evidence can be crucial in lending weight to an extraordinary claim.

Certain fields, like clinical medicine and psychology, offer more structured frameworks for evaluating evidence. In these domains, the strength of evidence is often gauged through rigorous statistical analyses. For example, a medical study might determine the efficacy of a new drug through numerous clinical trials involving thousands of patients. The collective results, if consistently showing the drug’s benefits over existing treatments, could be considered “extraordinary evidence” of the drug’s effectiveness.

Moreover, in these fields, the definition of “extraordinary” can be somewhat standardized. There are established benchmarks for statistical significance, effect sizes, and confidence intervals. These statistical measures offer a quantifiable means to judge the quality and quantity of evidence. They serve as a guard against potential biases and provide a way to determine if observed effects are likely genuine or just the result of random chance.

In essence, while the concept of “extraordinary evidence” remains somewhat nebulous in broader contexts, fields rooted in empirical research have developed tools and methodologies to bring clarity and objectivity to the evaluation process. The challenge, then, is not just in finding or producing extraordinary evidence, but also in understanding and interpreting its implications correctly.

Sagan Standard: Extraordinary Claims Require Extraordinary Evidence
Sagan Standard: Extraordinary Claims Require Extraordinary Evidence

Tracing the Roots of the Sagan Standard

While Sagan made the principle famous in his works, the idea has older roots. David Hume’s 1748 essay suggested that truly exceptional claims needed equally exceptional proof. Marcello Truzzi had also phrased the standard similarly before Sagan.

Historical records showcase similar sentiments expressed by other scholars over centuries. For instance, Pierre-Simon Laplace in the early 1800s said that proof for a unique claim should match its novelty. Thomas Jefferson once remarked on the need for stronger evidence for phenomena outside known natural laws.


M. Özgür Nevres


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