Transformational Grammar is a theory of grammar that focuses on how sentences can be transformed into different structures while maintaining their meaning. Developed by Noam Chomsky in the 1950s, it emphasizes the underlying rules that govern sentence formation. This approach helps linguists understand the complexities of language and how people generate sentences in their minds. The theory distinguishes between deep structure and surface structure. The deep structure represents the core meaning of a sentence, while the surface structure is the way that meaning is expressed in a specific language. Transformational rules allow for the conversion between these structures, illustrating the flexibility of human language.