When I took syntactic theory, Ivan Sag said something that seemed mysterious at the time but now, after working through a book on formal language theory, makes a great deal of sense. He said that older syntactic theories were working with mathematics from the 40s and 50s and were basically sophisticated string rewrite systems. What did he mean? The transformational grammars were based on context-free grammars of the variety inspired by Emil Post’s work. These enable one to take a string and apply a series of generation rules that change the string. When combined with transformation rules, one can change the order of substrings in a stirng, including adding in null elements. There is no deeper structure to it that this however.