Cromwell's rule

Etymology
Named by statistician Dennis Lindley, in reference to, who wrote in 1650: "I beseech you, in the bowels of Christ, think it possible that you may be mistaken."

Proper noun

 * 1) A rule stating that the use of prior probabilities of 0 or 1 should be avoided, except when applied to statements that are logically true or false, so as to leave room for the possibility that something very unlikely is in fact the case.