Phrases with «to know for certain»

I changed more than one variable from giveaway to giveaway so I don't know for certain what worked and what didn't. (tobecomeawriter.com)
«We don't know for certain what triggers asthma in cats,» he notes. (articles.chicagotribune.com)
As the listings have been removed a few hours after going live, we still don't know for certain if these special editions will be released or not. (geekreply.com)
(see all sentences)