This document presents a definition of phrases and describes a general approach to developing a theory of grammar based on universal grammar and native speaker intuitions. It defines phrases as groups of words that do not contain subjects or verbs. It then outlines a theory of grammar involving lexical categories that form phrase heads and phrase structure rules that determine phrase constituents and their orderings. Several phrase structure rules are provided for noun phrases, verb phrases, prepositional phrases, and adjectival phrases as examples.