 A different sort of objection to intuitions as a source of a priori evidence assumes that a source of justification must be capable of being calibrated to determine whether it is accurate (Cummins 1998: 116–118). What we see through a telescope justifies us in believing that the moon has mountains because we have done things like looking through telescopes at distant mountains on earth and then gone to them and discovered that the telescopes presented an accurate picture of the mountains. But what, the objection goes, can intuitions be checked against? Other intuitions? But that is like checking a crystal ball against itself.