What's a empiricist or a priori
Empircists -- including John Locke and David Hume -- believe that knowledge comes "a posteriori" or post experientially. In other words, if I bang my head of the roof going down a stairwell, the next time I will know not to jump down the last few stairs. For empiricists the existence or non-existence of things must conform to the principles of public verifiability. Not all that different from the positivist view of knowledge being exposed to the principle of falsifiability -- same thing really. "A priori" knowledge was/is believed by the likes of rationalists such as Rene Descartes. Basically "a priori" -- pre-experiental -- knowledge is knowledge that is, paradoxically, existent before I know it. So in the same stair situation if I bang my head off the roof, and know not to do it again, I'm merely remembering what I already knew, because that knowledge was with me before I experienced it.
I dont think that is what any agnostic claims. Its just when you ask him if he knows whether there is a God or knows if there is not a God, he'll just shrug his shoulders and say "I dont know".
No, I agree, that's not what they would SAY or acknowledge BELIEVING. However,
theist/atheist: Is there a god?
agnostic: I don't know
theist/atheist: Why don't you know?
agnostic: I don't know, becuase I don't know.
theist/atheist: So you don't know because you don't know?
agnostic: yes.
theist: So if you don't know because you don't know then how do you know?
agnostic: I don't.