-고: And, With No Claim About Why

-고 is the plainest connector Korean has. It attaches to any stem, needs no vowel decision, and means and.

What makes it worth a page is what it does not say.

Building it

Strip 다, add 고. That is all.

먹다   →  먹고
가다   →  가고
싸다   →  싸고
공부하다 → 공부하고

No consonant/vowel choice, no irregulars, no ㄹ behaviour. It is the most cooperative ending in the language.

Two jobs

Listing — both things are true:

싸고 맛있어요. — It’s cheap and tasty.
이 방은 넓고 밝아요. — This room is spacious and bright.

Sequence — one after the other:

씻고 잤어요. — I washed and went to bed.
밥을 먹고 갔어요. — I ate and then went.

Adjectives list. Actions sequence. You do not have to decide which — the verbs decide for you.

The contrast that matters

Compare with -아서/어서:

밥을 먹고 갔어요.     I ate, then went.        (two things, in order)
밥을 먹어서 갔어요.   I ate, so I went.        (the meal is the reason)

-아서/어서 ties the two halves together — as cause, or as one action setting up the next. -고 makes no such claim. It puts two things side by side and leaves the relationship to the listener.

The clearest case:

은행에 가고 돈을 찾았어요. — I went to the bank. I withdrew money. (two separate things)
은행에 가서 돈을 찾았어요. — I went to the bank and withdrew money there. (one connected event)

The second is what you almost always mean. Which is why learners who default to -고 for everything end up sounding oddly disjointed.

Use -고 when the link really is just “and.”

Tense sits on the last verb

밥을 먹고 갔어요. ✅
밥을 먹었고 갔어요. △

The past marker on the final verb covers the whole sentence. 먹었고 is not wrong, but it frames the two events as separately completed rather than as one sequence, and it is heavier than most sentences need.

Where -았/었고 earns its place is a genuine list of completed things:

밥도 먹었고 커피도 마셨어요. — I ate, and I had coffee too.

Not 그리고

그리고 also means “and” and is not interchangeable.

밥을 먹었어요. 그리고 커피를 마셨어요.   ✅  joins sentences
밥 그리고 커피                          ✗   never between nouns
밥하고 커피                             ✅

그리고 links sentences. -고 links clauses inside one sentence. Nouns take 과/와, 하고 or (이)랑.

Putting 그리고 between two nouns is one of the most common English-transfer errors, and it reads as clearly broken.

Soft spoken -고요

Clause-linking -고 can also land at the end of an answer with polite 요 — 카드도 사고요 — softening or adding a beat. That spoken habit is -고요, not a second listing connector.

-고 있다

Same ending, fixed construction — see -고 있다 for the progressive page:

먹고 있어요 — I’m eating.
기다리고 있어요 — I’m waiting.

Worth learning as its own pattern rather than deriving it from the connector.