To know a proposition, is it necessary that one is able to rule out every possibility of error associated with that proposition? Notoriously, infallibilism about knowledge—as defended, for example, in early work by Peter Unger (1975)—demands just this and argues on this basis for the skeptical conclusion that knowledge is rarely, if ever, possessed. Intuitively, however, the answer to this question is "no," in that in everyday life we only demand that knowers rule out those error-possibilities that are in some sense relevant. For example, to know that the bird before me is a goldfinch, I may be required to be able to rule out that it is not some other bird that could be in the area just now, like a jackdaw, but we would not normally demand (at least not without special reasons) that I be able to rule out the possibility that...