X' theory was a major milestone in the history of the development of generative grammar.1 It enabled important insights to be made into the phrase structure of human language, but it had a number of weaknesses, and has been essentially replaced in Chomskyan generativism by Bare Phrase Structure (BPS), which assumes fewer theoretical primitives than X0 theory, and also avoids several of the latter’s weaknesses. However, Bare Phrase Structure has not been widely adopted outside the Minimalist Program (MP), rather, X0 theory remains widespread. In this paper, we develop a new, fully formalized approach to phrase structure which incorporates insights and advances from BPS, but does not require the Minimalist-specific assumptions that come with BPS. We formulate our proposal within Lexical-Functional Grammar (LFG), providing an empirically and theoretically superior model for phrase structure compared with standard versions of X0 theory current in LFG.
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