Take, for instance, the following claims:
We all agree that the English determiners include words like the, a, this, some, any, and my, and we agree that these have two things in common which justify a cover term‘determiner’:At times, here, he's clearly talking about a category of words:
(2) A singular countable common noun normally needs a determiner in order to be grammatical, e.g. I heard *(the) dog.
(3) Only one determiner is possible per common noun, e.g. I heard *the my dog.
These two characteristics are what distinguish determiners from adjectives, and make the traditional classification in terms of ‘demonstrative adjectives’, ‘possessive adjectives’ and so on completely inappropriate.
The resulting word class is quite heterogeneous semantically. (pp. 8 & 9)
- proposing a list of words (by the way, we don't all agree that my is in the same class with those other words; it's a pronoun)
- contrasting with adjectives
- mentioning "word class"
Similarly, if you claim a limit on a common noun of one x, again x must be a function. If you say, for instance, that a head noun can't have other nouns (a category), it's entirely unclear what you mean. If you say it can't have any nouns functioning as complements, then you're probably right. If you say that it can't have any nouns functioning as modifiers, then you're almost certainly wrong. It's not the category of noun that makes the difference but its function.
If you you're confused about whether x is a category or a function, then trying to argue that x doesn't exist won't really make much sense.
Hudson, R. A. (2004). Are determiners heads? Functions of Language, 11(1), 7–42. doi:10.1075/fol.11.1.03hud