Sagan Standard
The principle that extraordinary claims require extraordinary evidence, scaling the strength of proof to the implausibility of a claim.
Also known as: Extraordinary claims require extraordinary evidence
Category: Principles
Tags: principles, critical-thinking, reasoning, epistemology, scientific-method
Explanation
The Sagan standard is the aphorism "Extraordinary claims require extraordinary evidence," popularized by the astronomer and science communicator Carl Sagan. It holds that the amount and quality of evidence needed to justify belief in a claim should be proportional to how surprising or implausible that claim is against our existing understanding of the world.
Mundane claims fit comfortably within what we already know and need only ordinary support to be accepted. A claim that overturns well-established knowledge, by contrast, competes against a large body of prior evidence, so it must clear a correspondingly higher bar before it becomes rational to believe. The more a claim would force us to revise, the stronger the evidence it must muster.
The principle is closely related to a Bayesian view of belief: a low prior probability demands especially strong evidence to shift a conclusion toward acceptance. Sagan's phrasing echoes earlier statements by thinkers such as Pierre-Simon Laplace and David Hume, but Sagan made it a touchstone of scientific skepticism in the twentieth century.
The Sagan standard is a practical guard against credulity, especially toward paranormal, pseudoscientific, or sensational claims. It does not forbid revolutionary ideas; it insists only that they be supported in proportion to their reach, so that genuine breakthroughs earn acceptance while unsupported extraordinary assertions do not.
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