The theist believes in a god or gods while the atheist denies this belief and all others like it. In my opinion the word belief is too ambiguous. It is fine if one defines it as “an acceptance that a statement is true or that something exists”, but too often it is used to mean something a little more open ended such as “trust, faith, or confidence in someone or something” or "an attitude positively oriented toward likelihood.” When defining “Atheist” and “Theist”, I would prefer using the words "absolutely convinced" and "not absolutely convinced" instead of the words "believe" and "don't believe". I’m not certain, however, that there are not some who would profess to think they can believe without being convinced of it ... hmm? So, maybe "believe absolutely" and "do not believe absolutely" would be sufficient.
Gnosticism is from Ancient Greek: gnostikos "having knowledge". A Gnostic purports to have knowledge that god exists while an agnostic is one who believes that there is currently insufficient evidence to determine the existence of any deity. An agnostic will still always fall into the category of a theist or an atheist, also being an agnostic simply means they are admitting they don't know for sure that their viewpoint is true. In a strict philosophical sense, some scholars would argue that we are all agnostics about everything because we can never truly know anything, including our own existence. Some current definitions of the word Gnostic has it to mean "can be known" and to me, this seems to be too ambiguous and relies on belief - "I believe it can be known" or “I'm convinced someday we'll know ". You either "know" (or think you know) by evidence or you "don't know" by lack of evidence. To eliminate the ambiguity I prefer to use “know (or think you know)" and "doesn't know".
So, as you see, we have two groupings, one for belief and one for knowledge:
Atheist: Does not believe absolutely that a god or gods exist.
Theist: Believes absolutely that a god or gods exist
Gnostic: knows a god or gods exist (or thinks he/she does).
Agnostic: does not know a god or gods exist.
With these, everyone should fall into one and only one of the four categories:
1. Agnostic Atheist: does not know and does not believe absolutely that a god or gods exist.
2. Gnostic Atheist: knows (or thinks he/she knows) that there is no god or gods and does not believe absolutely that a god or gods exist.
3. Agnostic Theist: does not know there is a god or gods but believes absolutely a god or gods exist.
4. Gnostic Theist: knows (or thinks he/she knows) that a god or gods exist and believes absolutely that a god or gods exist.
With these labels, I think you would have to be delusional if you thought you were either 2. (Gnostic Atheist) or 4. (Gnostic Theist). Regardless, they have the BOP (burden of proof) in showing sufficient evidence to support their claim. I would bet, or at least hope, most people, if honest with themselves, would be in the category of 1. (Agnostic Atheist) or 3. (Agnostic Theist). In fact, I would not be surprised if most people considered themselves agnostic atheists using the above definitions, assuming close introspection and honesty. It would be interesting, I think, to take a poll having people choose one of these for themselves, but not reveal the name of the label when taking the poll:
Choose the one answer that best fits you:
1. I do not know (can't prove) if a god or gods exist and I do not believe absolutely that a god or gods exist.
2. I know (can prove) that a god or gods do not exist and I do not believe absolutely that a god or gods exist.
3. I do not know (can't prove) if a god or gods exist and I do believe absolutely that a god or gods exist.
4. I know (can prove) that a god or gods exist and I do believe absolutely that a god or gods exist.
Lejandro, Look up many of the past discussions here you will find many answers to questions you did not know you had.
It is possible to be an anti-theist. This can be misunderstood to mean one who is against theist, I do not know any atheist that uses it in this context. What I am speaking of is the definition that is used by atheist. That is one who is anti=against religion. I am against religion in general as it can be detrimental to any culture. A common argument is that churches do good. That is often true they do organize coat drives food drives etc. The thing is religion is not necessary for altruism. We literally can be "good without God." There is no wrongs that make a right. Feeding children is GREAT! That does not justify "god" sending religious people to murder their parents for not believing in a particular faith or religion.
What you do understand to be true concerning a godhead is important. If you are unsure that is O.K. I think it is important to explore what Atheist, Agnostics and theist have to say and even more important to follow you mind as opposed to you heart. Our hearts leave us with things like that bad relationship we had. My worst was with Jesus, It was just one sided as he did not exist.