I argue that the well-known islandhood of adjunct prepositional phrases does not substantially derive from their adjuncthood. Instead, islandhood of these domains derives from various factors that are orthogonal to the argument/adjunct distinction, including PP-internal structure, lexical properties of prepositions, and semantico-pragmatic construal. To show this, I demonstrate that PP-islandhood cross-cuts the argument/adjunct distinction. In particular, (i) PPs with NP complements are generally not islands, (ii) PPs with tensed clausal complements are generally (strong) islands, and (iii) PPs with gerundive complements are generally (weak) islands. These generalizations hold whether or not the relevant PP has a prototypical adjunct function.

I identify an empirical limitation in Chomsky’s (2013, 2015) labeling theory and propose a theoretical modification that solves that problem. Chomsky argues that a labeling indeterminacy blocks movement of wh -subjects from Spec,TP into Spec,CP. However, I give evidence that wh -subjects can move from Spec,TP to Spec,CP. To solve the labeling problem, I propose (a) that labeling applies to the transferred constituent (normally the phase head complement), rather than the full phase, and (b) that labeling can be delayed by one application of Transfer. This proposal preserves core aspects of labeling theory, without requiring a costly complementizer deletion operation for wh -subject extraction.