Sagan Standard
"Extraordinary claims require extraordinary evidence." - Carl Sagan
Overview
The Sagan Standard states that the burden of proof increases with the implausibility or significance of a claim. If a claim challenges well-established knowledge (e.g. the laws of physics, or widely confirmed scientific theories), it requires stronger and more rigorous evidence than ordinary claims.
While Carl Sagan popularised the phrase—particularly in his book Cosmos (1980) and later in The Demon-Haunted World (1995)—the idea itself traces back to earlier thinkers, including David Hume, who argued in the 18th century that testimony for miracles must be weighed against the improbability of the event itself.