The Unique Groundability of Temporal Facts

The A‐theory and the B‐theory advance competing claims about how time is grounded. The A‐theory says that A‐facts are more fundamental in grounding time than are B‐facts, and the B‐theory says the reverse. We argue that whichever theory is true of the actual world is also true of all possible worlds containing time. We do this by arguing that time is uniquely groundable: however time is actually grounded, it is necessarily grounded in that way. It follows that if either the A‐theory or the B‐theory is actually false, then it is necessarily false.