In this paper, I argue that content of some presuppositions is determined dynamically. In particular, it is shown that the presupposition of want in control constructions depends on the interpretation of an action in the complement clause. Different presuppositional content of sentences with want is argued for using new and known observations about licensing of Polarity Sensitive Items. I propose to capture the dynamic nature of the presupposition of want using the AGM paradigm for belief revision (Alchourrán, Gärdenfors & Makinson 1985). Finally, I show that sensitivity to the interpretation of an action as intentional versus accidental is not specific to polarity system, but can be found across different domains of the grammar in many unrelated languages.