A sentence containing disjunction in the scope of a possibility modal, such as (1a), gives rise to the free choice inference in (1b). This inference presents a well known puzzle in light of a standard treatment of modals and disjunction (Kamp 1974 and much subsequent work). To complicate things further, free choice tends to disappear under negation: (2a) doesn’t merely convey the negation of (1a), but rather the stronger dual prohibition reading in (2b). There are two main approaches to the free choice-dual prohibition pattern in the literature, based on implicature and homogeneity. We present experimental findings that favour the homogeneity approach, and further discuss how the implicature approach could be developed to account for the results.

(1) a. Sue is allowed to buy the boat or the car.
b.Sue is allowed to buy the boat and Sue is allowed to buy the car

(2) a. Sue is not allowed to buy the boat or the car.
b. Sue is not allowed to buy either one

(based on joint work with Lyn Tieu and Cory Bill)