What's the difference between an adjective's adverbial form and continuative form?

Question

http://www.guidetojapanese.org/learn/complete/adverbs http://www.guidetojapanese.org/learn/complete/verb_sequences <-also covers adjectives

Following Tae Kim's guide, those two forms of 青黒い are

(adverbial form): 青黒く
(continuative/て-form): 青黒くて

In English, an adverb is used to modify a verb, an adjective, or another adverb. But in my previous thread, What conjugation of what word is ぐろく?, 「青黒く」 is also referred to as the "continuative form" meaning "bluish-black and".

So now I have to ask, what's the difference between these two forms? If both the adverbial form and the て-form can be continuative... then how can I tell if a word is meant to modify an upcoming verb/adjective or just link to it?

Example:

空は青ぐろく、一面の星がまたたいていました。

Adjective/Adverb: 青ぐろく
Upcoming Verb: またたいていました

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I would've read that sentence as "As for the sky, the stars all around were bluish-blackly twinkling", with the adverb modifying the next verb.

But it was translated by l'électeur as "The sky was bluish-black and the stars all around were twinkling", with the adverb not modifying the upcoming verb at all, just linking to it.

Can someone clarify the difference between a "true adverb", an adjective's adverbial form, and an adjective's て-form?
And why an adverbial form can be continuative?

Answer 1

Joining two statements

Broadly speaking, the く ending allows the meaning of the first statement to broadly modify the second, while くて puts an end on the first statement and separates it more from the second statement.

Let's look at the specific sample sentence in the linked thread.

「空{そら}は青{あお}ぐろく、一面{いちめん}の星{ほし}がまたたいていました。」

Here, we basically have two clauses. Simplifying drastically, we have:

「空{そら}は青{あお}ぐろい」

... and:

「一面{いちめん}の星{ほし}がまたたいていた」

Joining with the ~くて conjunctive form

We could join these two using the conjunctive くて form of the adjective in the first clause:

「空{そら}は青{あお}ぐろ​[く]{●}[て]{●}​、一面{いちめん}の星{ほし}がまたたいていました。」

The sense with this kind of joining is that the first statement finishes, and then the second statement comes in. It works well for connecting two statements that don't necessarily have a lot to do with each other. Part A, and then Part B. Kinda like:

"Here at Channel 7 News, our cameras are new​, and you'll get traffic info too!"

Looking again at our sample Japanese sentence and translating to try to give the flavor of this kind of joining:

「空{そら}は青{あお}ぐろ​[く]{●}[て]{●}​、一面{いちめん}の星{ほし}がまたたいていました。」
The sky was blue-black, and [separately, unrelatedly] the stars were twinkling all around.

Given the content of Part A and Part B, this kind of hard break doesn't seem to work very well -- the two statements are actually closely related. Which brings us to the く style of joining statements.

Joining with the ~く adverbial form

Without the て, as you noted, the adjective is technically in the く adverbial form. This can apply conceptually in a way to the following clause, essentially describing a quality of what comes next. Instead of Part A, and then Part B, it's more like Part A describes something more about Part B. There is no natural grammatical analogue in English, but to make it more explicit, we might break it down like this:

「空{そら}は青{あお}ぐろ​[く]{●}​、一面{いちめん}の星{ほし}がまたたいていました。」
With the sky be​ing blue-black​ly​, the stars were twinkling all around.

Here, the first part about the color of the sky more clearly leads into the second part about the stars.

That's horrible English and not how any native speaker would write it, but I hope that shows better how the Japanese fits together.