("A comprehensive grammar of the English language")Paganini was a great violinist. .
My daughter is training as a radiologist.
We found Lisbon (to be) a delightful city.
What a miserable day (it is)!
Whereas the indefinite article is required in the previous examples, there is vacillation in the following cases:
her duties as (a) hostess
my appointment as (a) lecturer
Jung as (a) thinker
Do they mean it's not necessary to use 'a' in the last three sentences? But they are countable nouns. What does that mean? Or do they act as titles/ranks in this case?