How does transformational grammar relate active and passive sentences?

In Noam Chomsky’s transformational grammar, active and passive sentences are related by deriving them from the same underlying structure rather than converting one actual sentence into another.12

The process relies on transformational rules that operate on the deep structure generated by the phrase-structure component. For example, a string such as "the + man + will + hit + the + ball" serves as the underlying input. When the passive transformation is applied, it permutes the elements—rearranging the noun phrases and adding auxiliary components like "be" and "en"—to produce the passive surface structure, such as "The ball will be hit by the man."123

By using these rules, the grammar formally demonstrates that sentences appearing different on the surface share a similar underlying relationship. While kernel sentences are generated without optional transformations, nonkernel sentences like passives are formed through the application of specific optional and obligatory transformational rules to the same base structure.123