This paper proposes a new explanation for the oddness of presuppositional and negative islands, as well as the puzzling observation that these islands can be obviated by certain quantificational elements. The proposal rests on two independently motivated assumptions: (i) the idea that the domain of manners contains contraries and (ii) the notion that degree expressions range over intervals. It is argued that, given these natural assumptions, presuppositional and negative islands are predicted to lead to a presupposition failure in any context.

What licenses the use of a definite description? The formal and philosophical literature has approached this question in two ways. The uniqueness approach (Frege, 1892; Russell, 1905; Strawson, 1950) holds that we may use a definite determiner only if the property denoted by its complement holds of exactly one individual in some domain: Sentence (1) and (2) can only be true if there is exactly one king of France, and exactly one American governor, respectively. Since this is not the case (...) in the actual world, the sentences are either false or (on most modern accounts) fall prey to a presupposition failure. (shrink)