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A sentence by a famous prize-winning writer: Sometimes she'd drop a syllable or two in a stanza's last or penultimate line in order to create the effect of a choked throat, or that of unwitting awkwardness caused by emotional tension.

In English, when we use an uncountable noun (usually uncountable), we don't use an indefinite article, but SOMETIMES when we use adjectives, or that-clauses, to modify that 'dictionarily' uncountable noun, an indefinite article is not omissble. In the above sentence, do you think AN should be placed before UNWITTING?

If not, then is there any idiomatic rule that I can follow when deciding whether I need A/AN before an uncountable noun?

I once heard from a teacher who said that noun should be an emotive noun, but I don't think this reason can stand, because in English we can say:

The Sun has been obliterated from the sky, and an unlucky darkness invades the world.
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A further example in which we can add A/AN:

The poems in those books had a diary-like intimacy and immediacy.
Sorry for making disconnected posts, but it's because I am going through a paperback to hunt down examples:

Since the name of the current was 'love', the poems about the homeland and the epoch were shot through with almost inappropriate intimacy;similarly, those about sentiment itself were acquiring an epic timbre.

Why not AN this time?
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I would say it's a matter of sense rather than idiom. The writer speaks of the effects of two things, a choked throat and awkwardness. She did not mean the effect of a single instance of awkwardness but the effect of awkwardness.
Johnson13A further example in which we can add A/AN:The poems in those books had a diary-like intimacy and immediacy.
You could drop the article in this one. The difference in sense is slight. The poems had a certain quality. The poems had traits. You can use other qualifiers, too: the poems had that intimacy you see in a diary, they had the intimacy of a diary.

The qualifiers pull the reader into the writer's circle. They say, "You know what I mean."
Johnson13Sorry for making disconnected posts, but it's because I am going through a paperback to hunt down examples:Since the name of the current was 'love', the poems about the homeland and the epoch were shot through with almost inappropriate intimacy;similarly, those about sentiment itself were acquiring an epic timbre.Why not AN this time?
The article would limit the intimacy to one particular kind, at least semantically, and that's not what the writer means. "Shot through" implies that scattered throughout the poems were instances of intimacy.
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Thanks.

A sentence: In a more general sense, ethics slip into a dependence on aesthetics.

Does it mean exactly the same as

In a more general sense, ethics slip into a dependence that is on aesthetics.
According to Oxford, Cambridge, Macmillan and Longman, UNWILLINGNESS is uncountable.

But I don't think the following sentence can be rewritten as my previous post says:

An unwillingness to accept reality, motivated not only by ethics but by aesthetics as well, is something unusual in Russian literature.

Surely we can't say AN UNWILLINGNESS WHICH IS TO..., right?