This topic corresponds to the post ""Strong" and "Weak" Atheism" of the SMRT group that can be found here:
Some confusion exists amongst those theists who choose to criticise atheism by targeting the positive claim that God does not exist, calling it "faith-based." At the same time, they assert that those who do not make this claim, and merely point out that there is no physical evidence for any god, are agnostic by the definition of the term.
However, the term "atheist" has developed in recent times to encompass both: those who assert that God does not exist, and those who assert merely that there is no evidence in favour of the hypothesis. No matter the historical definition of the word, it is now used as an umbrella term for both viewpoints.
The authors personal understanding is that those who assert the positive claim "there is no god" allege that their assertion is warranted due to the fact that a personal god, such as the one described by the Abrahamic religions, would have a noticeable and measurable effect on reality. When phenomena that should demonstrate such effect (such as the efficacy of prayer) are studied, they consistently fail to demonstrate it. Thus, an assertion of non-existence is considered warranted.
They often fail to take into account, however, that this does not disprove a more generalised theistic god: it merely disproves the properties given to the hypothesised deity by it's adherents.
This means that, for example, the god of the Young Earth Creationists (also known as YHWH) can be positively said to not exist: there are demonstratable effects that this deity should have on the universe that are not observed. However, the god of the theists or deists cannot be disproven in this manner, as it's effects on the universe are far more negligible and thus cannot be predicted: warranting the 'weaker' form of atheism: i.e. One has no reason to believe in it, but one cannot state with certainty that the deity in question does not exist.
Thus, the 'strength' of disbelief has more to do with the god in question than the individual. Many atheists are highly agnostic on the subject of the deistic god, while at the same time being certain of the non-existence of the "literal" god of the bible, which makes many testable claims which have, time and again, failed to hold up to scrutiny.*
*Examples would be the efficacy of prayer, the many scientific and historical discrepancies with regard to creationism, the flood of Noah, and other specifically mentioned biblical events, and the lack of any verifiable supernatural activity in natural history.
