Atheist vs Agnostic

Definitions

I feel that I should include some clarification of atheism and agnosticism because I get asked

"Why are you an Atheist and not just an agnostic?"

In fact many theists are actually taught to ask this, they are encouraged to tell those who proclaim themselves as atheists that unless they can prove god does not exist then they are just agnostics. It gets old quick, especially when you push back and they realise that they are actually agnostic, but you are still an atheist.

Theism is about belief - If you believe in a god you are a theist. If you dont believe then you are an atheist.

Gnosticism is about knowledge (claimed or actual)- If you have knowledge of god you are a gnostic. If you have no knowledge of god you are agnostic. Knowledge itself works either ways, knowing he does exist or knowing he doesn't.

Combinations

So these terms are actually separate things that can exist in combination:

1. A "Gnostic Theist" is someone who believes in god and knows that he exists.
   You're typical evangelical preacher who can look you in the eye and honestly tell you he hears the voice of god fits this description.
2. An "Agnostic Theist" is someone who believes in god but does not know god.
   Most people of faith that I meet fit into this category, they dont hear voices, they believe but they dont know. If you accept that it's possible there might not be a god no matter how strong you believe, this is you. 
3. An "Agnostic Atheist" is someone who does not believe in god and does not know god.
   This fits the vast bulk of atheists, they reject the claim of god but cannot say they have absolute knowledge that goes does not exist.
4. A "Gnostic Atheist" is someone who does not believe in god and knows that he does not exists.
   This is the more strident form of atheist, sometimes describing themselves as "anti-theists".  

GOD               I believe            I dont believe             NO GOD

<---------------|-----------------||------------------|---------------->

Gnostic Theist    Agnostic Theist    Agnostic Atheist    Gnostic Atheist

Believing the opposite

Just as theism is a belief, atheism is the absence of a belief - It is NOT however the same as the belief in the opposite.

For example:

A man appears on the Monty Hall show and has got up to the point where he now needs to choose between the money or the box.

• The box may contain money
• The box may contain a goat
• The box may contain some other prize

Now this mans wife tells him to take the box, she believes the box has the keys to a new house.

In fact everybody in the crow seems to have their own idea of the whats in the box and no two are the same.

The man does not belief the box contains the keys for a new house. He does not know what is in the box. But that doesn't mean he believes the box does not contain house keys. He cannot see inside the box, he cannot feel the weight of the box, he cannot hear any sound from the box.

He cannot say his wife is wrong, because he does not know what is the box, but if you ask him if the box contains a house he cannot honestly say yes either.

If a house had never been given out as a prize then the man could go a step further and say he has a reasonable expectation that is does not contain house keys.

What's more, if the box is replaced with an envelope and the man is able to feel the envelope he may feel comfortable in saying that what he feels is actively inconsistent with a house key.

This is the position most atheists find themselves in. The claim of the existence of god (or the house key) has no evidence, so it can not be accepted. When we do look for evidence we find it lacking or contradictory so we can have a reasonable expectation that god (or the key) does not exist. However we still have no absolute proof we have not yet opened the metaphorical box.