I think the whole agnosticism vs. atheism definition thing has been best summarized by the following graph, courtesy of the mighty Bud Uzoras of Dead Logic:
As an atheist, my degree of agnosticism varies depending on the god-concept being presented. I also think that most reasonable people would concur that we ought to value epistemic humility – just a fancy way of saying "there's a lot I don't and possibly can't know, so I could be wrong". I think most reasonable people would likewise concur that accordingly, we cannot be "absolutely certain" about anything. But we can be reasonably certain, often to a degree of very high confidence.
So with that said, I consider myself a strong atheist with regard to the Christian conceptualization of
God. In my view, that God is:
- Based upon a text of dubious historical authenticity that is replete with a self-defeating and logically absurd theology (at least as it is generally interpreted)
- Ascribed with logically contradictory and/or incoherent properties
- A failed hypothesis in explaining any known natural phenomenon
But let's say we define God differently. Let's say that since the principles of logic are derived from observation of physical reality, there's no reason why a God who exists beyond our reality ought to be bound by such laws. Personally, I'm inclined to believe that if there is a God, that's a more apt description. However, such a being is in principle permanently beyond our "epistemic horizon"; we cannot use science or logic to infer anything about this being, including its mere existence. So I can't say that I am reasonably certain such a being doesn't exist – I must hold a higher degree of agnosticism. But I can also say that such a God, while certainly possible, is essentially irrelevant to the human experience because it is unknowable. Absent any evidence or relevance to my existence, I can see no reason to hold a positive belief in this being – so I am a weak atheist with regard to this nebulously defined deity.
Atheism is strictly descriptive, not normative. It's not a philosophy or a world-view. And although it's closely intertwined with metaphysical naturalism, it is not the same thing. But while we may, in a broad sense, define atheism as a lack of belief in gods, I think most of us do take a bit stronger stance with regard to clearly defined concepts. Where does that leave the burden of proof? That depends. Supernatural things can always be defined in a way that they are epistemically useless, like the aforementioned nebulous God. Saying something like "I saw a miracle, and you cannot prove I didn't" is nothing more than defining the supernatural in a manner that permanently escapes rational scrutiny – it's defining the concept into irrelevance. The inability to conclusively disprove some abstract, nebulously defined concept does not give us sufficient grounds to deem it worthy of consideration – the burden of proof is quite clearly on the theist. But if I argue the points I listed above regarding the Christian God, then clearly the burden of proof is on me to justify those points through evidence and argument. That sort of contextually specific "strong atheism" is something that I think we non-believers ought to be more than happy to embrace.