Additional historical explorations leave on doubt that explict relative clause marking has lost ground over the last few centuries and that "American English" has been leading this development for at least 150 years both British and American English ,and in line with the Complexity Principle, the complexity contrasts associated with different choices of antecedent expression and relative clause subject types are shown to be matched by corresponding contrasts in terms of grammatical explicitness with the most complex environment favoring why or that and the least complex learning toward the zero variant