Learn Hardcore Korean: sasil oneul hoeuineun gilji anhasseo. - Actually, today’s meeting wasn’t long.

사실 means “actually” or “in fact.” It frames the sentence as a clarification or mild correction of an expectation. You can place it at the start, as here, or later (e.g., 오늘 회의는 사실 길지 않았어) with similar meaning. Using 사실은 adds a stronger topical/emphatic “as a matter of fact” feel.

Why is the topic marker 는 used on 회의 instead of the subject marker 가?

Using 회의는 sets “the meeting” as the topic and often implies contrast (e.g., “As for the meeting, it wasn’t long,” maybe unlike something else). 회의가 길지 않았어 is a plain statement focusing on the meeting as the grammatical subject, with less contrastive nuance. Both are correct; choose based on emphasis.

Could I mark 오늘 with 은 instead? What changes?

Yes:

오늘 회의는 길지 않았어: Topic = the meeting (today’s one). Contrast may be about the meeting versus other things.
오늘은 회의가 길지 않았어: Topic = today. Contrast may be about today versus other days. Both are natural; pick the topic you want to highlight.

Why not use the object marker and say 회의를?

Because 길다 (“to be long”) is a descriptive verb (adjective-like) that does not take an object. The meeting is the subject/topic of the state of being long, so use 회의가/회의는, not 회의를.

What does the -지 않다 construction do, and how is it different from 안?

Both negate the predicate:

-지 않다 is the analytic negative form, slightly more neutral/careful.
안 + verb/adj is an adverbial negation, a bit more colloquial and concise. Here:
길지 않았어 and 안 길었어 both mean “wasn’t long.” The -지 않다 form is more common and natural with many descriptive verbs like 길다.

Is 안 길었어 natural?

It’s grammatical and understandable, and many Koreans will say it. However, for adjectives like 길다, -지 않다 (길지 않았어) tends to sound more natural/neutral, especially in careful speech. In casual talk, 안 길었어 is fine.

What’s the nuance difference between 길지 않았어 and 길지는 않았어?

길지 않았어: simple negation (“it wasn’t long”).
길지는 않았어: adds a contrastive/concessive feel (“it wasn’t long, at least,” often implying “but [something else]…” like “but it was boring/annoying”).

How is 길지 않았어 built morphologically?

길-지 않-았-어

길-: stem of 길다 (“long”)
-지 않-: negative auxiliary (“not”)
-았-: past
-어: informal polite level (plain casual here without 요) Present negative: 길지 않아. Polite: 길지 않았어요. Formal: 길지 않았습니다.

How do I pronounce 않았어 and 회의?

않았어: commonly pronounced [아나써] (the ㅎ is silent here, and ㄴ links).
회의: both [회의] and [회이] are standard; many speakers say [회이]. So 회의는 ≈ [회이는]/[회의는].

Is it natural to use 길다 for the duration of a meeting? Should I use 오래 걸리다 instead?

Both are natural but slightly different:

회의가 길다/길지 않다: describes the event as (not) long in duration.
회의가 오래 걸리다/오래 걸리지 않다: focuses on how much time it took. For many contexts, they’re interchangeable. 오래 가다 (“last long”) is used more for states/effects; for meetings, 길다 or 오래 걸리다 is usually better.

Can I move the words around? For example, put 사실 later?

Yes. All are natural with small shifts in emphasis:

사실 오늘 회의는 길지 않았어.
오늘 회의는 사실 길지 않았어.
오늘은 사실 회의가 길지 않았어. Korean allows flexible adverb placement; keep topic/subject markers clear.

Why is it 않았어 and not 않었어?

The past marker agrees with the auxiliary 않다, whose stem vowel is ㅏ. So past is 않았-, not 않었-. Hence 않았어 is correct.

What register is this? How would I make it more polite or formal?

…않았어: casual (friends, younger people).
Polite: 사실 오늘 회의는 길지 않았어요.
Formal: 사실 오늘 회의는 길지 않았습니다. Add a question tone or …요? to ask politely.

Why is there a space between 길지 and 않았어?

Orthography rule: the negative auxiliary 않다 is written as a separate word after -지. So 길지 않았다/않았어 is spaced. Don’t write 길지않았어.

Do descriptive verbs like 길다 need a separate “to be” verb in the past?

No. Korean descriptive verbs already function as predicates. Past is made by adding the past marker (or, in negation, on 않다), so 길지 않았다 means “was not long” without any separate copula.

Do I need a plural for “meeting(s)” here?

No. Korean usually omits plural marking unless it’s important to specify. 회의 can refer to one or multiple meetings from context. If you really need plural, you can say 회의들, but it’s rarely necessary here.