“Theist”, “agnostic”, and “atheist” are not positions along the same continuum. They are actually answers to entirely different questions. A theist believes in at least one god, whereas an atheist doesn’t. An agnostic believes one cannot have knowledge of gods (including knowledge of their non-existence), whereas a gnostic (for lack of a better word) believes one can. So consider the two questions below:
- Do you believe that any gods exist?
- Can we know anything about these gods for sure, including whether or not they exist?
Note that one need only lack belief to be an atheist, and one’s agnosticism (their negative answer to #2) doesn’t in any way address the first question. Someone can be an agnostic atheist or even an agnostic Christian. I am an agnostic atheist because I haven’t seen sufficient evidence for any gods and I think that gods are often defined in a way that makes their existence unverifiable even in principle. In other words, gods may exist, but there’s no way a human knows anything about them.
Note also that lacking belief isn’t the same thing as asserting that something isn’t the case. A famous example is Russell’s Teapot. There could be a teapot orbiting a distant planet as we speak. I cannot disprove that, but I see no reason to believe it. Thus I am an “atheist” with respect to the teapot (I don’t believe it’s there), but given the available information, I concede that no one can prove or disprove otherwise, so I refrain from making the claim that it doesn’t exist.