Abstract
In 1979 astronomer Carl Sagan popularized the aphorism “extraordinary claims require extraordinary evidence” (ECREE). But Sagan never defined the term “extraordinary.” Ambiguity in what constitutes “extraordinary” has led to misuse of the aphorism. ECREE is commonly invoked to discredit research dealing with scientific anomalies, and has even been rhetorically employed in attempts to raise doubts concerning mainstream scientific hypotheses that have substantive empirical support. The origin of ECREE lies in eighteenth-century Enlightenment criticisms of miracles. The most important of these was Hume’s essay On Miracles. Hume precisely defined an extraordinary claim as one that is directly contradicted by a massive amount of existing evidence. For a claim to qualify as extraordinary there must exist overwhelming empirical data of the exact antithesis. Extraordinary evidence is not a separate category or type of evidence--it is an extraordinarily large number of observations. Claims that are merely novel or those which violate human consensus are not properly characterized as extraordinary. Science does not contemplate two types of evidence. The misuse of ECREE to suppress innovation and maintain orthodoxy should be avoided as it must inevitably retard the scientific goal of establishing reliable knowledge.
Highlights
Over the past few decades the aphorism Bextraordinary claims require extraordinary evidence^ (ECREE) has been popularized
What is the nature of an extraordinary claim? What qualifies as extraordinary evidence? Should there be two standards of evidence in science? Is there any context in which ECREE can be invoked correctly? In the discussion that follows I argue that the true meaning and proper invocation of ECREE can be understood if its historical roots are traced
If ECREE is to have any intelligible meaning, it is best considered in the wording chosen by Carl Sagan
Summary
Over the past few decades the aphorism Bextraordinary claims require extraordinary evidence^ (ECREE) has been popularized. It has been called Ba fundamental principle of scientific skepticism^ (Voss et al 2014: 893) and Ban axiom of the skeptical. The modern roots of ECREE lie in the context of discussing paranormal phenomena (Sagan 1979), it has been used to discredit mainstream scientific hypotheses. In 2007, a group of geologists hypothesized that a large-scale comet or asteroid impact event in North America 12.9 ka caused the Younger Dryas cooling event. The evidence for this event is significant. What is the nature of an extraordinary claim? What qualifies as extraordinary evidence? Should there be two standards of evidence in science? Is there any context in which ECREE can be invoked correctly? In the discussion that follows I argue that the true meaning and proper invocation of ECREE can be understood if its historical roots are traced
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