||The key work in modal skepticism is Van Inwagen 1998. In this paper van Inwagen argues against extreme modal skepticism and in favor of moderate modal skepticism. He presents a key challenge to conceivability approaches, especially that of Yablo 1993. The criticism centers around the idea that in order for one to conclude that their conception provides adequate warrant for believing that a proposition is possible, their conception must have a certain grain of detail that is not easily defeasible by further facts. Often it is the case that our conception does not provide us of adequate warrant, because our conception is best explained by our ignorance of certain facts that are clearly relevant.