There are two kinds of atheism: strong (positive) atheism and weak (negative) atheism. The difference between these two is basically that a weak
atheist doesn't believe in God, while a strong
atheist believes in no God.
Weak atheism is essentially the same as
agnosticism. It states that since we have no proof of a God, we cannot know for sure that one exists. Strong atheism states that since we live in a scientific world where the existence of things is determined solely by their observability, we cannot assume anything unobservable to exist. God isn’t observable, therefore he doesn’t exist (
cf. Occam’s Razor). This doesn't mean that an atheist wouldn't WANT to believe in God, it merely means that he has no REASON to believe in it/him.
Strong atheists often question the special treatment weak atheists – and theists – give to
religion. If they believe that the tooth fairy or Santa Claus do not exist, why are they willing to give God a benefit of the doubt?
Strong atheism is often equated with
religion since it takes a strong stance on the issue. This is, however, fallacious.
Religion is not based on rationality, and strong atheists value rationality over fantasy. Therefore atheism is not parallel with
religion.