Dynamic logic of preference upgrade Johan van Benthem, Fenrong Liu Abstract: Statements not only update our current knowledge, but also have other dynamic effects. In particular, suggestions or commands `upgrade' our preferences by changing the current order among worlds. We present a complete logic of knowledge update plus preference upgrade that works with dynamic-epistemic-style reduction axioms. This system can model changing obligations, conflicting commands, or `regret'. We then show how to derive reduction axioms from arbitrary definable relation changes. This style of analysis also has a product update version with preferences between actions, as well as worlds. Some illustrations are presented involving defaults and obligations. We conclude that our dynamic framework is viable, while admitting a further extension to more numerical `utility update'.