 Preservation and Inclusion are the only norms that are really about revision–they capture the diachronic spirit of AGM revision. Inclusion says that revision by \(\alpha\) should yield  no more new beliefs than expansion by \(\alpha\). In other words, any sentence \(\beta\) that you come to believe after revising by \(\alpha\) is a deductive consequence of \(\alpha\) and your prior beliefs. Consider the following principle: