Phrase structure grammar consists of rules that generate natural language sentences. Example: S-> NP+VP VP -> V+ NP NP -> Det + Noun V -> Aux + Verb Det -> the, a, an,--- Verb -> catch, eat, write, --- Noun -> Police, teacher, ---- Aux -> will, can, is, ---- Transformational grammar is a set of Transformation rules , which transform one phrase- maker(underlying) into another phrase-maker (derived) These rules are applied on the terminal string generated by phrase structure rules. These rules are used to transform one surface representation into another.