Sluicing and Constraints on Quantifier Scope

In each case, the meaning of the sluiced sentence approximates so closely the sentence in the preceding clause, that it is reasonable to expect it to have the same shape as that sentence – as indicated. And yet, the shape of the sentence in the first clause includes an island, as shown by the ungrammaticality of the a-cases. So why isn’t there an island violation triggered by wh-Movement out of the sluiced IP in the b-examples? There has been a renewed interest in this puzzle following the publication of Chung, Ladusaw, and McCloskey (1995). One of the interesting twists to the problem that they introduce is that the island effects reappear when the wh-phrase in the sluice matches an implicit argument in the antecedent clause, rather than an overt argument as it does in the examples above. Thus, there is a contrast between the b-examples of (1) and (2), and the cases below.