"Which book did you file ___ [without reading ___]?"
Not all subject islands are equally strong. Some violations become acceptable if they are "saved" by a second gap in the sentence, known as a . Islands
Extracting from a subject might simply be too mentally taxing for the brain to process in real-time. Exceptions and "Parasitic" Gaps "Which book did you file ___ [without reading ___]
Some researchers suggest the problem isn't grammar, but . Islands
The second gap is inside an "island," but the first "licit" gap makes the whole sentence feel okay to a native speaker.
Subjects usually provide "old" information (the background). Trying to pull a "new" focus out of a backgrounded subject creates a mental clash.