The compound nominal predicate denotes a certain state or quality of the subject, it`s a qualifying predicate.
The compound nominal predicate consists of two parts the link-verb and the predicative. The predicative names a state or a property. It serves to characterize the subject. It can be expressed by a word of any notional part of speech or by a phrase or a clause.
She is a doctor (noun)
She is beautiful(adjective)
Our task is that we should know grammar well. (Predicative clause)
Sometimes the predicative is expressed by an infinitive or a gerundial complex
E.g.The most important thing for us is to meet her .
The greatest trouble was our not knowing all the details.
The link-verb expresses different grammatical categories. It has no independent meaning and its function is to connect the subject with the predicative. It`s usually expressed by the verb to be but it can also be expressed by some other verb which loses its lexical meaning and acquires the abstract meaning of
1.Being(be, feel, look, smell, taste) (sound funny, burn dim, suck dry,)
2.Becoming(become, grow, get, turn) (to be called Bob, to be left alone,)
3.Remaining(remain, continue, keep, stay) (to be elected president)
4.Seeming and appearing(seem, appear) E.g.The weather turned cold.You look great.