THE USE OF ARTICLES WITH PREDICATIVE NOUNS AND NOUNS IN APPOSITION
1. As a rule, predicative and appositive nouns are used with the classifying indefinite article which shows that the speaker is characterizing a person, object or event as a specimen of a certain class of thing. With plural nouns no article is used:
She is really an excellent creature but a complete fool, as I said.
I had several companions and they have all been complete fools.
2. If there is a limiting modifier, predicative and appositive nouns are used with the definite article:
He is the only person here with medical knowledge.
Philip had been the hero of his childhood.
3. If predicative and appositive nouns denote the position (rank, state, post or occupation) which is unique, i.e. can be occupied by one person at a time, either no article or the definite article is used. These nouns are often used after the verbs to appoint, to choose, to elect, to become and some others:
Mr. Henderson is manager, not under-manager any longer.
His ideal was professor Edward Edwards, head of the Department of Chemistry.
They chose him chairman of the Society.
He was elected (the) President of the country.
The definite article tends to be left out in sentences like:
It was nearly 40 years before she became Queen.
When he was President he often longed for more privacy.
As some grammars point out, it would be unnatural to leave in the definite article and say “She became the Queen” or “When he was the President” though the article can be used when the noun is followed by of.
Note that when talking about a person rather than describing someone’s role you need an article: The Queen is strongly against the project.
Note the absence of article in set expressions with the verb to turn: to turn traitor, to turn miser, to turn pirate.
4. The nouns son and daughter predicatively and appositively generally take the definite article when modified by an of-phrase if they express mere relationship:
She is the daughter of a doctor.
If the speaker wants to emphasize the idea that there are several sons and daughter in the family, the indefinite article is used: She is a daughter of a doctor. When the stress is laid on the social position of the person in question, no article is used: She is daughter of a doctor.
5. No article is used in structures with enough where predicative nouns acquire
an adjectival character, denoting a certain characteristic of the person in question:
Surely Bella isn’t fool enough to believe that sort of stuff?
6. The article is also omitted when predicative nouns are used in clauses of concession with inverted word order: Child as he was, his judgement was sound.
7. If the appositive noun denotes a well-known person or work of art, the definite article is generally used: John Galsworthy, the famous English writer, was of a Devonshire family.
But if the person or work of article is not widely known, the indefinite article is used: “Pericles”, a comedy by Shakespeare, is hardly ever staged.