Phasehood as defective intervention: Possessor extraction and selective DP islandhood in West Circassian

Ā‐extraction of possessors in West Circassian is constrained in a puzzling way: the possessor of an ergative or applied argument DP may not undergo clausebound wh‐movement, but long‐distance possessor extraction across a clausal boundary is grammatical. Based on the variable islandhood of these DPs, this paper argues for an agree‐based approach to phasehood. Phase opacity is treated as intervention defective intervention, with the phase intervening between the probe and the goal. Defective intervention does not take place if the corresponding phase has independently entered an Agree relation with the movement‐triggering probe. Islandhood is thus correctly predicted to be contextually determined: in West Circassian, the difference between clausebound and long‐distance possessor extraction is conditioned by the set of agreement features on the local movement‐triggering probe: a wh‐feature on C in the case of clausebound extraction and a successive‐cyclic edge feature on embedded C in the case of long‐distance wh‐movement. Additionally, the account appeals to the opacity of phase edges to explain the contrast between DPs that display islandhood effects (ergative and applied argument DPs) and constituents that are uniformly transparent for subextraction (the absolutive DP and postpositional phrases).