If one does not believe in god(s), one is an atheist. Those who claim they are agnostic seem to think atheism is the claim that god(s) do not exist, when it is not.

@NothinnXpreVails Theism is a belief in God or gods. Atheism is lack of belief in God or gods. Gnosticism is a claim of knowledge about something, such as a secret knowledge of how to be saved. Agnosticism is the claim of lack of knowledge of something, such as the existence of God or gods. In essence, one concerns itself with belief and the other concerns itself with claiming knowledge. You can believe there is a God or gods and claim to know for sure. You can also believe in God or gods and claim not to know for sure. You can not believe and claim to know for sure, or not believe and claim not to know. They are separate issues, one dealing with belief/nonbelief and one dealing with a claim to knowledge/nonknowledge. This is why some people call themselves Agnostic Atheists. You may not make such distinctions yourself, but many people do.

@Heraclitus Your statements about belief/disbelief vs knowing/not knowing strike me as completely contradictory. Seems to me neither can know, but both belief and disbelief can be accompanied by not knowing.

@Rossy92 So where's the contradiction?

@Heraclitus My bad. Your wording threw me. I initially thought you were saying the first 2 examples we are able to do, but the second 2 we are not able to do. I think we're basically on the same page except I'm not sure what you mean by "You may not make such distinctions yourself, but many people do." I would just add that I find the unequal application of the term Agnostic to describe non-believers vs believers to be annoying, and feel the label is often unnecessary and useless.

@Rossy92 Well, you could throw out that last sentence of mine. I was being polite. But, what I was getting at was that, for example, some people insist that agnostics are nothing more than closet atheists because they don't recognize the distinctions that I enumerated previously. I tend to agree with you about annoyance/confusion about using the term agnostic to sometimes apply to both believers and nonbelievers. But there is a reason behind that. It used to be that theists (at least those that I knew) did not claim to have absolute knowledge of God because where there is absolute certainty there is no need for faith. You don't need faith that one plus one equals two, you just know it. So theists, who lived by faith, took this to be a denial of faith, or more accurately perhaps, a denial for the need for faith and consequently an undercutting of the message of the Gospel as they saw it. But things have changed. Nowadays people claim to know God directly all the time. Some will even tell you they know God exists because they talked to Him last night...and even that He talked back. (Again, where is the need for faith if you already know?) But, not all theists claim such absolute knowledge or certainty. They will tell you that they don't know that there is a God, but take it on faith that there is a God. Such a theist might be called an agnostic theist, though it can be a confusing (or annoying) claim. An agnostic atheist, by contrast, does not live by faith but by evidence. Hope this clarifies.