Of a particularly relevant note here is agnosticism [1], or the viewpoint that there are certain things that are simply unknowable to humans. The implication being that humans can neither confirm NOR deny the truth value of the statements. Metaphysical statements often fall into this category. And hence, you can also have agnostic theists [2] and agnostic atheists [3], who both recognize that they are taking a stance on an unknowable truth value. Some would then define this as the very essence of the word faith, but I would like to at least point out that both sides are subject to the same definition.
[1] http://en.wikipedia.org/wiki/Agnosticism