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Time to post what Martin called "the Scriven extension principle"
(though in the hardback edition of "Atheism", this is misprinted on
p.283 - I have corrected it to be consistent with earlier versions):


   A person is justified in believing that X does not exist if (1) all the
   available evidence used to support the view that X exists is shown to be
   inadequate; and (2) X is the sort of entity that, if X exists, then
   there is a presumption that there would be available evidence that would
   be evidence adequate to support the view that X exists; and (3) this
   presumption has not been defeated although serious efforts have been
   made to do so; and (4) the area where evidence would appear, if there
   were any, has been comprehensively examined; and (5) there are no
   acceptable beneficial reasons to believe that X exists.
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