This somewhat speculative and exploratory paper will argue that the labels of phrasal categories (e.g., VP versus NP) are not needed in syntactic theory. In other words, no operation or condition may be defined that makes reference to VP versus NP. An immediate consequence of this proposal is that bar-levels, such as X' versus XP, are impossible to define. This paper can be seen as an extension of the program, begun in Chomsky's 1994 paper "Bare Phrase Structure," to derive X'-Theory from more basic principles.
Collins, Chris. 2002. Eliminating Labels. In Samuel Epstein and Daniel Seely (eds.), Derivation and
Explanation in the Minimalist Program, 43-64. Blackwell.