Theism is saying "I believe there is a god."

Atheism is saying "I believe there is no god."

Agnosticism is saying "I don't know if there is a god."

Gnosticism is saying "I know if god exists."

So, there are four categories of people when it comes to religious beliefs:

• Agnostic atheist: the most common type of atheist. They argue that the burden of proof is on the person who claims god exists, and since they consider that there is no evidence for the existence of god, they believe there is no god.

• Agnostic theist: also the most common type of theist (at least in Europe). They also admit that they don't know if god exists or not, but they believe that he does. They often disagree with the notion that the burden of proof is on them to prove god exists, arguing instead that the burden of proof is on whoever is making the god, be it that god exists, or that it doesn't.

• Gnostic atheist: a minority within atheists. They claim to know that god does not, in fact, exist. One of the main arguments for this position is the problem of evil, which can be stated in this question: "If God is all powerful, all knowing and all benevolent, why does evil exist?" Gnostic atheists also believe that god doesn't exist because they consider themselves capable of disproving the exists of every god that has ever been described in all of history.

• Gnostic theist: also a minority, though larger, amongst theists. They claim to know god does exist, and their arguments are varied. The ontological argument states that, being god perfect, he exists because existence is a part of perfection, so anything that is perfect must also exist. This argument is mainly used by philosophers, and is considered by many to be a fallacy of circular argument (where the conclusion is already implied in the premises of the argument). Another proof that gnostic theists provide is that our existence is improbable, and that therefore, there probably exists a higher being who made us (either directly as creationists believe, or indirectly through fine tuning of the universe's variables). This type of theist also relies often on physical evidence of god (his intervention in the universe), such as the holy scriptures, miracles or answered prayers (this last one is more personal, so you won't hear anyone arguing this because only they experienced it).