When practicing scientists are reminded of these straightforward points, they frequently adopt what the philosopher George Berkerley called a “forlorn skepticism.” From the idea of science as certain and infallible, they jump to a cynical description of their endeavors. Science is sometimes held to be a game played with arbitrary rules, an irrational acceptance of dogma, an enterprise based ultimately on faith. Once we have appreciated the fallibility of natural science and recognized its sources, we can move beyond the simple opposition of proof and faith. Between these extremes lies the vast field of cases in which we believe something on the basis of good—even excellent—but inconclusive evidence.