Is "a" used properly here?

I'm not sure why you have all the phrases in quotations, but unless they are actual quote of the professor, I wouldn't use them. Here is what I would write, hope it conveys the message you want to send.

First, I am surprised a professor would fail to see the merit in Professor Root-Bernstein’s accusation of plagiarism, especially since the plagiarizer (your former student) has already admitted and issued an apology to the offense.

Thank you Ceili.

Your reply has implied explicitely that the usage "a" is not proper there?

yes

Sometimes we use the same word for the act or practice, in writing, of committing (doing) something (usually bad) such as libel, blasphemy, plagiarism, misrepresentation, exaggeration, falsehood etc, and an instance of that thing. Words of this type can mean (without the article) the act or practice, or (with an article, pronoun or number) an example or instance of the thing.

So the word 'plagiarism' can refer to

1. The act or practice of the verbatim copying or imitation of the language, ideas, or thoughts of another author and representing them as one’s own original work.

2. The material so appropriated.


In his essay Mr Smith is guilty of plagiarism, libel, misrepresentation, exaggeration, falsehood and blasphemy.

Mr Smith's essay contains a plagiarism, several libels, many misrepresentations, numerous exaggerations, a falsehood and a blasphemy.

In this case 'a' is unnecessary, but it is not incorrect. Calling it 'a' plagiarism would mean just one example, as opposed to more than one.

But that is precisely what the writer is expressing, one instance of plagiarism instead of plagiarism in general which might lead a reader to think that there was more than one instance, or worse perhaps, a paper wholly plagiarized, so the article "a" is necessary.

Normally though, when you accuse someone of plagiarism it's just the one instance.

Clearer.
Thank you all guys.