In the book 'the Cambridge Grammar of the English Language (CGEL)', the authors propose the theoretical framework used to describe the English sentences as shown below:
- Subject: NP
- Det: D → a
- Head: N → bird
- Predicate: VP
- Predicator: V → hit
- Object: NP
- Det: D → the
- Head: N → car
CGEL, page 26
To get the tree diagram above, the first step is to identify the constituents of the sentence with the constituency tests. The second step is to describe these constituents what grammatical categories (e.g.,N, D, NP) they belong to. And the last step is to further describe these constituents what grammatical functions (e.g. object, head, subject) they belong to.
The authors suggest I have to know what grammatical categories these constituents belong to before knowing what grammatical functions they belong to. However, when I try to follow this order, there seem to be some problems.
For example, I want to know what grammatical category the word 'dog' in the sentence 'the dog is smiling' belongs to. I suspect it might be a noun, so I turn to page 326 of the book where the properties of nouns are described. One of the properties of nouns is that it functions as 'head' of the noun phrase. My problem is: How am I supposed to know the grammatical function of the word 'dog' when the authors suggest that I first have to know its grammatical categories before knowing its grammatical functions?
Summary of defining properties of nouns
[Type] [Description] i INFLECTION Nouns prototypically inflect for number (singular vs plural) and for case (plain vs genitive). ii FUNCTION Nouns characteristically function as head in NP structure. iii DEPENDENTS Various dependents occur exclusively or almost exclusively with nouns as head: certain determinatives (a book, every day), pre-head AdjPs (good news), relative clauses (people who work). Conversely, nouns differ from verbs and prepositions in that they do not take objects: I dislike it but not *my dislike it.
CGEL, page 326