Many previous theories have proposed covert movement for both syntactic and interpretational purposes. In cases of overt movement, we often observe pied-piping—additional material dislocated together with the logically attracted material. In joint work with Hadas Kotek, I have investigated the question of whether covert movement also triggers pied-piping. Following previous work on the interpretation of overtly pied-piped constituents (Krifka, 2006; Cable, 2010), we propose the use of focus intervention effects (Beck, 2006) to diagnose the existence and size of covert pied-piping. The results show that covert pied-piping does exist, and that the constituent covertly pied-piped is the largest among those options for overt pied-piping.

• Kotek and Erlewine, 2016. “Covert pied-piping in English multiple wh-questions.”  
  Linguistic Inquiry 47:4, pages 669–693. DOI: 10.1162/ling_a_00226

Our diagnostic also shows that focused constituents which are pronounced in-situ in English undergo covert focus movement with pied-piping, as proposed previously in Drubig (1994), Krifka (2006), and Wagner (2006), contra Rooth (1985, 1992), as reported in a NELS proceedings paper. In more recent work, we have also developed additional, independent arguments for this approach.

• Erlewine and Kotek, 2014. “Intervention in focus pied-piping.”  
  Proceedings of NELS 43, volume 1, pages 117–130.

We have also applied our intervention effect diagnostic to study wh-words used as relative pronouns. We show that relative pronouns in English non-restrictive relatives are interpreted in-situ within their pied-piping constituents via focus alternative computation. We show that this supports the view that non-restrictive relatives are proposition-denoting, rather than property-denoting.

• Erlewine and Kotek, 2016. “The structure and interpretation of non-restrictive relatives: Evidence from relative pronoun pied-piping.”  
  Proceedings of the 51st Meeting of the Chicago Linguistic Society (CLS 51), pages 149–163.
• Kotek and Erlewine, 2016. “Intervention effects in relative pronoun pied-piping: experimental evidence.”  
  Proceedings of Sinn und Bedeutung 20, pages 448–461.
• Kotek and Erlewine, 2015. “Relative pronoun pied-piping in English non-restrictive relatives.”  
  Manuscript, National University of Singapore and McGill University.