ABSTRACT
Every possible phrase structure rule is derived from X in the general form Xi […Xj…], where (i) the dots stand for any number of categories of maximal complexity, and (ii) the indices i andj stand for the level of complexity of the category X and (iii) Xj cannot be more complex than Xi. Phrase structure rules like VP→A NP are ruled out by these constraints. The term ‘X-bar’ arises from the notation where one or more bars are placed above the constituent X to represent the levels of complexity. For that reason, the following notation may be used: X, X′, X″, X0, X1, X2, or X, , where the maximal projection can also be referred to as XP.
