Double Wh-Islands and Relativization
The analysis proposed here receives further support from the fact that D linked/specific wh-phrases, though extractable from infinitive/subjunctive indirect questions, exhibit ‘‘double wh-island’’ effects with infinitive/sub junctive indirect questions, as shown in (1).
(1)

As the derivation proceeds, we construct the matrix vP (vP1) phase (2).
(2)

In (67), covert restructuring (covert AspP-movement) applies twice. The D-linked/specific wh-phrase which assignment is required to move out of VP to the most deeply embedded vP-edge (vP3-edge) position in accordance with the Mapping Hypothesis. It cannot raise any further because of the economy condition, however, since its movement is not triggered by any formal feature at the intermediate vP-phase (vP2-phase) level or at the matrix vP-phase (vP1-phase) level. Which assignment is not accessible to operations at the matrix CP because of the PIC. There is no way of satisfying the uninterpretable EPP feature and Q-feature of the matrix C. This derivation crashes; the ‘‘double wh-island’’ effects follow.
The proposed analysis can also account for the fact that relativization behaves exactly like movement of a D-linked/specific wh-phrase with respect to the Wh-Island Constraint, as shown in (3) and (4).
(3)

(4)

As shown in (3a) and (3b), respectively, relativization may take place out of an infinitive indirect question but not out of a finite indirect question. Relativization out of an infinitive indirect question exhibits the ‘‘double wh-island’’ effects, as shown in (4). These facts also follow from the proposed analysis if we assume with Cinque (1990) that relative operators are specific, just like D-linked wh-phrases.