Hi Al,

I was just wondering if something called a 'tag exclamation' can be used with the indefinite or zero article. For example,

Johh, the utter fool, insisted on staying with them.

Note, that 'the utter fool' above is not an appositive, but a tag exclamation according to Longman Comprehensive grammar p. 1304. The book does not mention anything about other possibilities, i.e. can a tag exclamation be 'an utter fool', or 'utter fool' at all?

I haven't heard the term 'tag exclamation'. However, your sentence is certainly fine, and 'the utter fool' sounds surprising and thus rather exclamatory.

an utter fool - this also sounds fine to me.

utter fool - I'd say this is also acceptable, although a lot more uncommon and colloquial-sounding. I'd be inclined to write it in a phrase like John, utter fool that he was, insisted .  . .

Best wishes, Clive