That's not what I was talking about, interpreting "It's possible that X will happen" as "the event X is non-empty" is as wrong as interpreting "I believe X will happen" as "negation of even X is empty". Uncertainty is just lack of certainty, "it's possible" expresses probability lower than that of "it's probable", way below "it's certain". See also the references from the Possibility article on the wiki.