The Sagan Standard

The principle that “extraordinary claims require extraordinary evidence”.

The Core Principle

For a claim that appears highly improbable or contradicts well-established scientific understanding, a commensurate degree of proof is necessary before it can be accepted.

• Heuristic: It serves as a tool for scientific skepticism and rational inquiry.
• Burden of Proof: The burden of proof increases with the outlandishness of the claim.

Origin

Popularized by astronomer Carl Sagan in his 1979 book Broca’s Brain and his 1980 television series Cosmos. It echoes earlier philosophical thoughts by David Hume (“Of Miracles”) and Marcello Truzzi.

Practical Application

If a claim is “extraordinary” (i.e., highly unlikely given current knowledge), then the “standard” evidence (like hearsay or simple observation) is insufficient. Robust, verifiable, and high-quality data is required.

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