[1] Word classes, largely corresponding to traditional parts of speech (e.g. noun, verb, preposition, etc.
At least three criteria are used in defining syntactic categories: For instance, many nouns in English denote concrete entities, they are pluralized with the suffix -s, and they occur as subjects and objects in clauses.
For example, one informal means of determining if an item is lexical, as opposed to functional, is to see if it is left behind in "telegraphic speech" (that is, the way a telegram would be written; e.g., Pants fire.
X-bar theory, for instance, often sees individual words corresponding to phrasal categories.
In this context, the term lexical category applies only to those parts of speech and their phrasal counterparts that form open classes and have full semantic content.
In order to acknowledge such functional categories, one has to assume that the constellation is a primitive of the theory and that it exists separately from the words that appear.
Early research suggested shifting away from the use of labelling, as they were considered to be non-optimal for the analysis of syntactic structure, and should therefore be eliminated.
In line with both Phrase Structure Rules and X-bar theory, syntactic labelling plays an important role within Chomsky's Minimalist Program (MP).
Chomsky first developed the MP by means of creating a theoretical framework for generative grammar that can be applied universally among all languages.