Conversation so far:
what are the main principles of generative-syntax (grammar)
Generative grammar is a linguistic theory that regards linguistics as the study of a hypothesised innate grammatical structure.
who developed the theory of generative grammar
The theory of generative grammar was developed by Noam Chomsky.
when was the theory of generative grammar developed
The theory of generative grammar was developed in the 1950s.

Question: what is an application of the theory
Self-contained rewrite: what is an application of generative grammar