Although faith is usually associated with deities and other mythologies, certain varieties of atheism must also be considered a kind of faith (though merely being the void where a religious faith would otherwise be). Theoretically, there can be four several varieties of atheism/theism: gnostic atheism (the belief that no deities exist alongside the claim that this non-existence can be known from the evidence): gnostic theism (the belief that one or more deities exist alongside the claim that this existence can be known from the evidence); agnostic atheism (the belief that no deities exist but which also claims that the existence/non-existence of such is unknown or cannot be known); and agnostic theism (the belief that one or more deities exist but which also claims that the existence/non-existence of such is unknown or cannot be known, Immanuel Kant being an example of this rarer type of theist). Gnostic theism and gnostic atheism are often simply called "theism" and "atheism" in general paralance, though both agnostic atheism and theism do exist (the latter simply tend to be less vocal about their views). Both agnostic and gnostic belief in atheism or theism, in turn, can be understood as strong (positive) or weak (negative) in form: for example, positive gnostic atheism makes the claim that we have positive evidence against the existence of deities, whereas negative gnostic atheism makes the claim that due to a lack of evidence (due to a negative) we can discount the possibility that deities exist on probable grounds. Positive gnostic theism would make the claim that we have positive evidence for the existence of deities, whereas negative gnostic theism makes the claim that due to a lack of evidence for strong gnostic atheism (due to a negative) we can accept that deities exist on probable grounds. Strong agnosticism would make the claim that in principle we cannot know of the existence/non-existence of deities, while weak agnosticism makes the claim that we lack enough evidence to make a decision on rational grounds.
As there is currently no determining evidence to back strong/weak gnostic theism, strong/weak atheism, or strong agnosticism, they all must be considered faith systems. (Unfortunately, there are still a great number of gnostic Theists and Atheists on the Web that fight over who is right, although by definition, neither side can be considered correct). Weak Agnosticism, however, can currently be considered the sole rational postion (the theistic or atheistic beliefs which happen to be associated with it currently having no bearing on the question), as no side has any proof, proving Weak Agnosticism by default.