A occurs when the grammatical subject of a sentence acts as one of these barriers. In English, you can usually extract a word from the object of a sentence, but doing the same to the subject results in an ill-formed "island violation".
Modern theories suggest certain phrases are "phases" that become invisible to the rest of the sentence once completed. 2. The Information Structure View Islands
Extracting from a subject might simply be too mentally taxing for the brain to process in real-time. Exceptions and "Parasitic" Gaps A occurs when the grammatical subject of a
Subjects usually provide "old" information (the background). Trying to pull a "new" focus out of a backgrounded subject creates a mental clash. Trying to pull a "new" focus out of
Once a subject moves to its final position, its internal structure is "frozen" and cannot be accessed.
The second gap is inside an "island," but the first "licit" gap makes the whole sentence feel okay to a native speaker.
"Which book did you file ___ [without reading ___]?"