learn many things from experience, and infer, that the same events will always follow the same causes. By this principle they become acquainted with the more obvious properties of external objects, and gradually, from their birth, treasure up a knowledge of the nature of fire, water, earth, stones, heights, depths, &c., and of the effects which result from their operation. (Hume, David S. "Concerning Human Understanding" Section IX, 83.)
Augustine's discussion of Grace versus free will is especially interesting. There are several points in Augustine's arguments which rely on some sort of ambiguous, undefined concept to support a "we can't understand god" type of mentality. One prime example of this is Augustine's explication of the trinity. The trinity represents unity yet three distinct avatars of god. This understanding of the trinity is an amorphous understanding of omission. It runs something like this: we can't understand the trinity by human rationale, but through an intense and encompassing belief-investigation, we can come to terms with this seeming paradox.