Some people draw spurious distinctions between the pair “gnosticism” / agnosticism and theism / atheism, saying that the former concerns “knowledge” while the latter, “belief.”
But “belief” is not “blind faith without evidence”; it’s a very normal and everyday intellectual phenomenon: an assent to a proposition. Further, knowledge is often defined in philosophy (not entirely correctly, but let’s not worry about that now) as justified true belief. Knowledge and belief are not independent of each other. One cannot know P without giving mental assent to, i.e., without extending belief to, P.
I suggest rather that the gnostic / agnostic distinction regards contemplative life, wherein proofs of God’s existence or non-existence are entertained for the edification of all concerned.
The theist / atheist distinction regards the active life.
Here’s the key difference: when speculating, one can assume anything and see where the assumptions lead him. One need not actually believe anything, and the assumption may be false, as long as it is useful or reasonable to assume it.
When acting, one must base his plans on true beliefs, regardless of evidence for or against them. If one is building a bridge, then one is ipso facto extending assent or beliefs to a vast number of (hopefully) true propositions in math, physics, etc. It may be that the builder is using a controversial theory in his project. Despite the fact that many scientists hold this theory in contempt, all is forgiven as long as the bridge works.
Thus, if you live your life without relying on God in any way, then you are a (practical) atheist. If, in building a life for yourself (and not just a bridge), you do not depend on anything God-related, regardless of any speculative disputes about any proofs of God’s existence, you’re an atheist. If you resolve in your heart: things of God “have no use to me, and so I make all my plans without regard to them,” then you are a confirmed atheist.
Further, the distinction between agnostic theists and agnostic atheists is uninteresting in philosophy. The discussion proceeds between
1) those who think there is a proof of God’s existence;
2) those who think there is a proof of God’s non-existence; and
3) those who are unsure but are capable of contributing to the debate by taking, in a purely speculative way, at one point one side, and at another the other side, as matters appear to them.
Whether the agnostic is in addition a theist or atheist is his own personal life — as in, paying heed to God or ignoring gods — is his own business and no one else’s.
Being unconvinced by arguments either for or against God’s existence makes one an agnostic. If one also lives his life without worrying about God (or gods, or unicorns), then he is demonstrating his atheism to all concerned. But that’s an arbitrary lifestyle choice of one’s own personal career. It has no value for the speculative question of whether God exists.
If one is an agnostic, both atheism and theism are choices in the same manner as the choice of preferred ice cream flavor. For example, one might lean toward agnostic theism simply out of overabundance of caution, as per the Pascal’s wager. Only if one is a “gnostic” is he ineluctably moved toward belief by evidence either for or against God’s existence. I’m not concerned here to analyze Pascal’s wager, only to point out that the two distinctions fall into the two axes of the division of life into active and contemplative.