Learn Hardcore Korean: sueobeul deutdaga gapjagi inteonesi kkeunhgyeosseoyo. - While attending the class, the internet suddenly got disconnected.

수업을 듣다 literally means “to attend a class” or “to listen to a lecture.” When you attach -다가 to a verb stem, it indicates that the first action was in progress and then something else happened (often unexpectedly).

수업을 듣다가 → “While I was attending class…”
It sets up background action 1 (attending class) and leads into action 2 (internet got cut).

How is -다가 different from -고 있었다(가) or -고 있다?

-고 있다 simply marks a continuous/progressive state:
“수업을 듣고 있어요.” → “I’m attending class.”
-고 있었다 is its past counterpart:
“수업을 듣고 있었어요.” → “I was attending class.”
-다가, on the other hand, emphasizes that while that action was happening, something else interrupted or followed:
“수업을 듣다가 친구가 왔어요.” → “While I was in class, my friend came.”
Use -다가 when you want to highlight the interruption or shift from action 1 to action 2.

Why is the subject omitted in 수업을 듣다가? Who is doing the listening?

In Korean, if the subject is clear from context (especially I or we in daily conversation), you can drop it. Here, the speaker is obviously talking about themselves:

(저는) 수업을 듣다가… → “(I) was attending class and…”
Omitting the pronoun makes it more natural and less repetitive.

What part of speech is 갑자기, and what’s its role in this sentence?

갑자기 is an adverb meaning “suddenly.” It modifies the verb clause that follows, signaling that the internet cut off happened without warning. You can place it:

before the verb: 갑자기 인터넷이 끊겼어요.
or even before the whole clause for emphasis: 수업을 듣다가 갑자기 인터넷이 끊겼어요.

Why is 수업 followed by 을 in 수업을 듣다가?

The verb 듣다 (to listen to; to attend) is transitive—it requires an object. The object 수업 (class/lecture) takes the object particle 을:

수업을 듣다 → “to attend class”

What’s the nuance of the verb 끊겼어요, and why not 끊었어요?

끊다 is the active verb “to cut off” or “to disconnect.”
끊기다 is its passive/intransitive counterpart: “to get disconnected.”
Using 끊겼어요 focuses on your perspective (“My internet got cut off”) rather than you actively cutting it.
Saying 인터넷을 끊었어요 would mean “I cut off the internet,” which changes the meaning.

Can you use 끊어졌어요 instead of 끊겼어요? What’s the difference?

끊어지다 also means “to be cut/disconnected,” but it often describes physical objects breaking (e.g., a rope snapping).
For network or connection failures, 끊기다/끊겼어요 is more idiomatic.
You’ll rarely hear 인터넷이 끊어졌어요; stick with 끊겼어요.

What politeness or formality level does the ending -었어요 indicate?

The -었어요 ending combines past tense -었- with polite informal speech -어요. It’s called the “요”-form polite style, suitable for speaking with strangers, colleagues, or in casual business settings. It’s respectful without being overly formal.