No Crystal Balls

Abstract

A crystal ball, in Hall’s (1994) sense, need be neither round nor crystalline. The world is said to contain crystal balls whenever the present carries news of the as-yet-undetermined parts of the future. Images appearing in spheres made of magical quartz might be crystal balls, in the relevant sense, but so too might arrangements of magical tea leaves or neural states in the brains of time-travelers or clairvoyants. Many philosophers believe that crystal balls are metaphysically possible. In this essay, I argue that they are not.