 Preservation says that, so long as the new information \(\alpha\) is logically consistent with your prior beliefs, all of your prior beliefs survive revision by \(\alpha\). In the setting of non-monotonic logic, we called this principle Rational Monotony. All objections and counterexamples to Rational Monotony from  Section 2.1.1  apply equally well in belief revision. As we have seen, Preservation rules out any kind of  undercutting defeat of previously successful defeasible inferences. Accepting both Preservation (rational monotonicity) and Inclusion (conditionalization) amounts to saying that when confronted with new evidence that is logically consistent with her beliefs, a rational agent responds by simply forming the deductive closure of her existing beliefs with the new evidence. On that view, deductive logic is the only necessary guide to reasoning, so long as you do not run into contradiction.