In an attempt to account for every sentence that could possibly appear in a language, noam chomsky developed psr's, otherwise known assuch as > np + vp.
1 phrase, paradigm, or preposition
2 structure, synonym, or sentence
3 reaction, rule, or regulation

In an attempt to account for every sentence that could possibly appear in a language, Noam Chomsky developed PSR's, otherwise known as 
1) PHRASE
2) STRUCTURE
3) RULE

PSR is identified as a type of rewrite rule wherein the syntax of a given language is closely associated with the early stages of transformational grammar. PSR was proposed by Noam Chomsky in 1957.