 There appears to be no change in the body of Einstein’s evidence when he is simply doing some derivations and calculations. But the limiting case of no new evidence seems to be just the case in which the new evidence E is trivial, being a logical truth, ruling out no possibilities. Now, conditionalization on new evidence E as a logical truth changes no credence; but Einstein changes his credences nonetheless—and rightly so. This is called the problem of old evidence, formulated as a counterexample to the Principle of Conditionalization.