Adjunct clauses are traditionally assumed to be strong islands for extraction across languages. However, the universal island status of adjunct clauses has been challenged by studies showing that extraction is possible from finite adjunct clauses in the Mainland Scandinavian languages. The possibility of extraction in these languages appears to be affected by various factors, including the type of adjunct clause, the type of extraction dependency, and the presence of contextual facilitation. These findings call for a re-evaluation of the islandhood of adjunct clauses in English. We conducted an acceptability judgment study on relativization from three types of finite adjunct clauses in English (if-, when-, and because-clauses) in the presence of supporting context. We found that the three clause types showed rather non-uniform acceptability patterns: extraction from when- and because-clauses both yielded significantly lower ratings than extraction from if-clauses, which patterned with non-island that-clauses. Our results suggest that at least for relativization, if- and when-adjuncts are not invariably strong islands in English, and that extra-grammatical factors may be key in understanding island structures traditionally assumed to be purely syntactic in nature.
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