  The idea of preserving conditional beliefs emerged recently as a new paradigm
apt to guide the revision of epistemic states. Conditionals are substantially
different from propositional beliefs and need specific treatment. In this
paper, we present a new approach to conditionals, capturing particularly well
their dynamic part as revision policies. We thoroughly axiomatize a principle
of conditional preservation as an indifference property with respect to
conditional structures of worlds. This principle is developed in a
semi-quantitative setting, so as to reveal its fundamental meaning for belief
revision in quantitative as well as in qualitative frameworks. In fact, it is
shown to cover other proposed approaches to conditional preservation.
