What is what if?

Abstract With literature and empirical evidence, this article argues against the existing claim that what if-questions are idioms and proposes that they are the result of the syntactic and semantic combination of what and if-conditionals. With further evidence, it is argued that what can be a propositional anaphor which occurs in different contexts, rather than being restricted to what if-questions. A formal characterization of the syntactic and semantic properties of the propositional what is formulated in the framework of Dynamic Syntax, demonstrating how this word makes semantic and syntactic contributions to the interpretation of utterances in English as a mechanism of interaction between interlocutors.