'The Problem of the Criterion: Is Knowledge too Hard or too Easy?' We acquire knowledge through methods such as perception and reasoning and, according to an intuitively plausible principle, acquiring knowledge through such a method requires us first to know that this method is reliable. But it has long been recognized that this seems to give rise to a vicious regress, making knowledge impossible. Rejecting the principle, on the other hand, seems to make knowledge too easy: we could come to know that a method is reliable by using that very method! So how might we solve this ancient puzzle? We acquire knowledge through methods such as perception and reasoning and, according to an intuitively plausible principle, acquiring knowledge through such a method requires us first to know that this method is reliable. But it has long been recognized that this seems to give rise to a vicious regress, making knowledge impossible. Rejecting the principle, on the other hand, seems to make knowledge too easy: we could come to know that a method is reliable by using that very method! So how might we solve this ancient puzzle?