What came first, the atheist or the theist?

[Edwardo Piet]

Then clearly we are using knowledge in two different syntaxes here.

I'll give you an example. A theist believes there is a God but that doesn't mean he 'knows' it because it obviously may not be true that God exists. However if he does 'know' it then that just means he believes in it + it is also true that God exists. He can't 'know' it if he doesn't also believe it.

@EvF: In that case, what would you call a lack of belief that is based upon a lack of any knowledge of the claim having been made? And, what would you call a lack of belief based upon knowledge of and the dismissal of the truth of a claim that has been made?

Lack of belief=disbelief. Disbelief has nothing to do with belief other than the fact it is what you call the state of not having belief.

Positively believing there is not a God and lacking belief in God is different.