He starts with the original Transformational-generative grammar in the late 50s, and then as more and more exceptions and complexities of language were found th

He starts with the original Transformational-generative grammar in the late 50s, and then as more and more exceptions and complexities of language were found that didn't fit neatly into the transformational-generative model, the theory was extended to account for these exceptions, creating the Extended Standard Theory (syntactic constraints, X-bar theory), later revised to Revised Extended Standard Theory (restrictions upon X-bar theory, complementizer). Then we've got the addition of the Principles and Parameters theory (head-initial, head-final) in the 80s, which led to the Minimalist program as things had started to get out of hand. https://en.wikipedia.org/wiki/Generative_grammar https://en.wikipedia.org/wiki/Generative_grammar https://en.wikipedia.org/wiki/Transformational_grammar https://en.wikipedia.org/wiki/Transformational_grammar https://en.wikipedia.org/wiki/X-bar_theory https://en.wikipedia.org/wiki/X-bar_theory https://en.wikipedia.org/wiki/Principles_and_parameters https://en.wikipedia.org/wiki/Principles_and_parameters https://en.wikipedia.org/wiki/Government_and_binding_theory https://en.wikipedia.org/wiki/Government_and_binding_theory https://en.wikipedia.org/wiki/Minimalist_program https://en.wikipedia.org/wiki/Minimalist_program