It has been known to me that a gerund can function as a noun and should or likely to be treated more as an uncountable noun than a countable noun.

Mixing of sugar and flour makes this dough ...

If you want to be specific, I think you could write:

The mixing of sugar and flour makes this dough ...

If you want to indicate the mixing being an instance of it or an example of it, you could write (I think) like this:

A mixing of sugar and flour makes this dough ...

It could be more clear if you write this though (but the above example seems to be correct grammatically too):

An instance of sugar and flour makes this dough ...

It has been to me that a quoted content (I may be wrong but what I call a quoted content is one that has quotation marks around it, whether or not they are done to quote someone's words or to highlight a word/words) can be treated an uncountble noun too.

"-ing" is not needed in your sentence. -- Just the mention of a case to highlight, I think.

The "-ing" is not needed in your sentence. -- Not just mentioning but specificallymentioning, I think.

A "-ing" is not needed in your sentence. -- An example of "-ing" use or an instance of "-ing" use, but this is what gives me trouble. I think whether a word in quotation marks can accommodate an indefinite article is predicated on whether its semantic meaning can embrace it.

So, I think I would be able to say, depending on words, some words that are in quotation marks can accommodate its having an indefinite article, whereas some words that are in quotation marks can't accommodate the use because its semantic meaning and how it is used in sentences make it awkward at best if not wrong to have an indefinite article. Sounds plausible?

Sorry for a long post.
Do you mean something like this?
An "I'm sorry" is not nearly enough. You're going to have to do a lot more than just apologize after what you've done!
Hi Believer,

In terms of common usage, both your examples work with both definite and indefinite articles - i.e., countable and uncountable. I'd say your interpretation of the situation is correct.

In the case of quotes, we observe the "a/an" switch, based on the way the letter would be spel(t): an "ing"; an "s"; a "t"; a "w."

The "mixing" examples are all good, and natural. (I once worked in a large bakery.) I can't imagine what "an instance of sugar and flour" might mean. You could say "the/a/an occurrence/combination of sugar and flour in the same recipe . . . " (I think you'd have to say, "an instance of sugar and flour being etc. )

Could you please provide examples of cases where you feel something in quotes could not be used with an indefinite artlcle because of its semantic meaning?

Best wishes, - A.

Edit. In Yankee's example, a definite article would also work, right?? The "I'm sorry" you gave me last night is not nearly enough.

P.S. Can anyone tell me if "instance" and "occurrence" may be used interchangeably?
Students: Are you brave enough to let our tutors analyse your pronunciation?
Yes, That sound like something I had in mind. The use of an indefinite article is what give me trouble sometimes. Thank you.
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Thank you, Avangi.

In my previous post, I should have used third-person verb tenses, 'sounds' and 'gives' -- proper subject-verb agreement wasn't made due to my carelessness.

Going back to your request for examples of cases where I would feel something in quotes could not be used with an indefinite article becauss of its semantic meaning, I would have say that I can't think of any at this point in time.

Do you think anything in quotes is good a candidate as a typical (known-to-be??) uncountable noun?

Thank you.
Hi Believer, I'm not brave enough or knowledgeable enough to give you a definitive answer. For starters, I'm not familiar with the implications of your expression, "a typical (known-to-be??) uncountable noun."

I think I can imagine situations where the semantic meaning of what's in quotes would have a bearing on it's "countable-ness," and others where it would not. In Yankee's example, the semantic meaning is an integral part of the meaning of the sentence. And yet by changing a few words in the sentence surrounding the quote (and leaving the quote untouched) we can change it from countable to uncountable.

- A.