 Whatever precisely is involved in knowing a fact, it is widely recognized that some of our cognitive successes fall short of knowledge: an agent may, for example, conduct herself in a way that is intellectually unimpeachable, and yet still end up thereby believing a false proposition. Julia has every reason to believe that her birthday is July 15: it says so on her birth certificate and all of her medical records, and everyone in her family insists that it is July 15. Nonetheless, if all of this evidence is the result of some time-keeping mistake made at the time of her birth, her belief about her birthday could be false, despite being so thoroughly justified. Debates concerning the nature of  justification[20]  can be understood as debates concerning the nature of such non-knowledge-guaranteeing cognitive successes as the one that Julia enjoys in this  example.[21]