His victory in the election is 'almost a certainty'. [=it is nearly certain/definite that he will win the election]
It is difficult to say 'with certainty' [=in a certain or definite way] which of the plays was written first.
Scientists still do not know with any degree of 'certainty' why the disease spread so quickly.
(..) some girls? Embarrass my friend? See, the sad thing about a guy like you is, in years you're gonna start doin' some thinkin' on your own. And you're gonna come up with the fact that there are two certainties in life. One: Don't do that. And two: You dropped grand on a fuckin' education... (..)1997 Good Will Hunting