Structural and semantic ambiguity of why-questions: An overlooked case of weak islands in English

We argue that English why -questions are systematically ambiguous between a purpose and a reason interpretation, similarly to Mandarin, Russian, and Polish (contra Stepanov & Tsai 2008). We argue that the distinct semantic interpretations correspond to two distinct base-generated positions of why. While reason why is base-generated within CP (Rizzi 2001, Ko 2005), purpose why is adjoined to vP (Stepanov & Tsai 2008). Furthermore, we show that English purpose why, similarly to previously reported data from Mandarin, is only compatible with dynamic predicates with agentive subjects. We argue that this selectional restriction follows from two properties: (i) why semantically requires a proposition as its argument, and (ii) only dynamic predicates with agentive subjects have a syntactic structure that accommodates two adjunction sites of the relevant semantic type, i.e., they contain two distinct propositional levels (Bale 2007) and therefore two attachment sites for why. In contrast, propositionally simple predicates only have one propositional level and hence only one possible attachment site, which corresponds to the reason interpretation of why. Evidence for this proposal comes from the observation that only the lower why - associated with the purpose reading - is sensitive to negative islands, which suggests that its attachment site is below negation (vP), whereas the higher why is insensitive to island effects of this sort, which suggests that its base generated position is above negation (CP).