Learn Hardcore Korean: oneul beoseuga neujeoseo nado jigakhaesseo. - Today the bus was late, so I was late too.

버스가 marks “the bus” as the grammatical subject and presents it as new or factual information: the bus was late.
버스는 would make “the bus” the topic and often adds contrast or emphasis (e.g., “As for the bus (today), it was late…”).
All of these are possible with slightly different nuance:
- 오늘 버스가 늦어서… (plain statement of cause)
- 오늘은 버스가 늦어서… (“today” is topical/contrastive)
- 버스는 늦어서… (contrastive “as for the bus”)

Why is it 늦어서 and not 늦었어서? Where did the past tense go in the first clause?

With the connective -아서/어서 (“because/so”), Korean usually puts the tense on the final verb of the sentence. So 늦어서 … 지각했어 is the normal pattern.
늦었어서 is generally avoided in standard usage and sounds awkward.
If you need explicit past in the first clause, switch to a different linker:
- 버스가 늦었기 때문에…
- Or split into two sentences: 버스가 늦었어. 그래서…

What exactly does -아서/어서 do here? Could I use -니까 or 때문에 instead?

-아서/어서 links a natural cause to its result and sounds neutral and matter-of-fact.
Alternatives:
- -니까: often a bit stronger or more reason-giving/justificatory.
- (으)므로: formal, written.
- 때문에 after a noun/nominalized clause: 늦었기 때문에 (more formal/explicit).
- Two sentences with 그래서: …늦었어. 그래서 … (very common in speech).
Note: -아서/어서 is generally not used directly with commands/suggestions.

What’s the difference between 늦다 and 지각하다?

늦다 = “to be late” in a general sense.
- 버스가 늦다 (The bus is late), 나 늦었어 (I was late).
지각하다 = “to be tardy (to a scheduled obligation)” like work/school/class.
- 회사에 지각했어, 수업에 지각했어.
In your sentence, 버스가 늦어서 (the bus was late) is the cause, and 나도 지각했어 (I was tardy) is the result.

Why is it 나도, not 저도?

Does 도 replace another particle? Should it be 나도가 or 나도는?

도 attaches to the noun and replaces case/topic particles in most everyday sentences.
- So use 나도 지각했어, not 나도가 or 나도는.
You can stack 도는/도도 in special emphatic/contrastive contexts, but that’s uncommon and can sound unnatural if misused.

Can I change the word order?

Yes. Korean word order is flexible; keep the final verb last. Examples:

Why not 늦게 here? What’s the difference between 늦어서 and 늦게?

늦어서 uses the verb 늦다 with -어서 to give a reason: “because (it) was late.”
늦게 is an adverb meaning “late(ly)” and modifies another verb.
- You could say 버스가 늦게 와서 나도 지각했어 (“because the bus came late…”).
늦게서 is incorrect; -게서 is not a causal connector.

Why is there no particle after 오늘? Can I say 오늘은?

Time words like 오늘, 내일, 어제 are often used without particles when they simply set the time.
오늘은 adds a topical/contrastive nuance (“as for today”) and is also natural if that’s your intent.

How are key parts pronounced in fast speech?

늦어서 → roughly [느저서] (the ㅈ sound surfaces as “j”).
지각했어 → roughly [지가캣서] (the ㅎ in 했 leads to a tense “ss” sound in -써).
버스가 → [버스가]. These are approximations; actual phonetics follow Korean liaison/assimilation rules.

Any spacing or spelling gotchas?

Could I use 그래서 instead of -어서?

Yes. Split it into two sentences:

버스가 늦었어. 그래서 나도 지각했어. This is very natural in conversation and clearly shows cause → result.

What does 나도 (“me too”) refer to here? Me too… what?

도 scopes over 나: “I, too.”
It usually implies someone else (e.g., classmates/coworkers) was late, or that there’s a prior context where others were late.
If you want to say “today too,” move 도: 오늘도 버스가 늦어서…
If you want “I did other things too,” you could say 지각도 했어 (but that changes the meaning to “I also happened to be late (among other things)”).

Is 지각을 했어 okay?

For the “tardy” meaning, people typically say 지각했어 without an object marker.
지각을 하다 appears in formal writing mainly with the academic “perception” sense of 지각(知覺), not “tardiness.” So stick with 지각하다 (no object) for being late.

Are there more formal or alternative ways to say “the bus was late”?

버스가 지연돼서… (“was delayed”) — neutral/formal.
버스가 연착해서… (“arrived late/delayed”) — more common with trains/planes, but can be heard for buses too.
All work with the same structure: … 돼서/해서 나도 지각했어(요).