Dave O, gotta disagree with your distinction (very respectfully of course).

I agree with JulieF. An atheist can legitimately say something elaborate like "To the best of my knowledge or as far as I can tell, there is no God. I am as certain of that as I think I need to be to make such a claim." The same atheist can also legitimately say in the interests of bevity, "I am certain that no such entity as a "god" exists in our universe."

NightWing, I used to profess agnosticism and once was an agnostic. But I finally realized that I was not uncertain. The question then was whether to be honest with myself and others that I might inform about my beliefs.