perspectives is an attempt to furnish hypotheses concerning prin­ ciples of phrase structure with some sort of independent justification. 1. PHRASE STRUCTURE THEORY: A BRIEF HISTORY A basic outline for a theory of phrase structure theory is accepted by all of the authors here; it is known as 'X-bar theory'. The concepts of X-bar theory are expressed in some form by a number of pre-generative linguists. For example, Bloomfield (1933) contrasted endocentric struc­ tures such as noun phrases and verb phrases with those he considered exocentric, e. g. prepositional phrases and clauses. Jespersen (1933), while presenting a functional system of description (in terms of 'ranks', where rank one is 'nominal', for example), clarified the relations among the head of a phrase, its modifier, and a phrase which modifies the modifier.