The philosophical interest of mystery is that something may well fall under a distinctive ontological concept of mystery. Such a thing would be explicable with reference to intention, but not uniquely determined by its explicans. This is the "properly mysterious," which is essentially mysterious in virtue of what it is, not just of our epistemic limitations. The richer uses of 'mystery', and defects in recent literature, suggest this line of inquiry. ;Part I rebuts the main arguments against the possibility that (...) something is properly mysterious. First, if something's existence is completely explicable it need not thus be exhaustively explicable . Second, event-determinism is not establishable empirically and nothing establishes general determinism a priori . So there is no reason to think every existent is uniquely determined to exist. But there is good reason to think everything is completely explicable in principle. ;Part II shows there is better reason to think the world's existence properly mysterious than not. The world asked about in the question "Why does the world exist?" should be defined as the totality comprising all that really changes and what is ontologically parasitic thereon . The World's existence is both logically contingent and contingent in one or the other of two de re senses , and thus is either inexplicable for any knower or explicable as intentionally produced. The producer would be extramundane, de re necessary, and could not uniquely determine the existence of The World. Defending classical theism against charges of conceptual incoherence, I conclude that the existence of The World is best thought completely explicable as intentionally created, though not exhaustively explicable by the existence of its creator. ;In conclusion, I expound and adopt Aquinas' account of creation, on which God creates for a reason and freely. Thus there is good reason for the world's existence, but no reason why this world exists rather than some other. (shrink)