 Note that, during his derivation and calculation, Einstein does not perform any experiment or collect any new astronomical data, so the body of his evidence seems to remain unchanged, only consisting of the old data. Despite gaining no new evidence, Einstein changes (in fact, raises) his credence in the new theory, and rightly so—against the usual construal of the Principle of Conditionalization. Therefore, there is a dilemma for that principle: when construed literally, it is too weak to prohibit arbitrary credence change; when construed in the usual way, it is too strong to accommodate Einstein’s credence change in the Mercury Case. This problem is Earman’s problem of old evidence.