Thank you, again.
Are these types of verbal nouns (as you called it) or instances of verbal nouns? What validates their placement of an indefinite article?
I did a Google
Book search for the what you seem to be callling "verbal nouns" -- watching, mixing, playing, shouting and seemed to have come up with these tidbits:
a watching of the clould and pillar
a watching of the sky
a mixing of the two stratified layers
a mixing of the systems
a mixing of molecules
a playing of
flutesa playing of a symphony
a shouting of
Songa shouting of patrotic sentiments
What do all indefiinte articles indicate? An instance of mixing, watching, playing and shouting? Or a type of watching, mixing, playing, and shouting?
To make into types, I think, you can do it two ways: 1) by setting them up attributively -- eg, adding adjectives to make one different from the other or 2) by
setting them up into types contextually -- like saying "Orange juice is a liquid."
Another way to validate the use of an indefinte article seems to be to make instances of them, like how we do with the word 'discussion' -- a discussion to mean an instance of it, whereas
discussion without the article to refer to it generally.