-고 vs -아/어서: What Is the Difference?

Key facts

• -고 means "and" or "and then." The two parts can be independent, and it also lists adjectives: 키가 크고 머리가 길어요.
• -아/어서 means "and then" when the first action sets up the second (go there and do it there), and it also means "because."
• Only -아/어서 can give a reason. -고 cannot: 비가 와서 안 가요 is "because of rain," while 비가 오고 안 가요 is not.
• The first clause of -아/어서 takes no tense marker, and the subject is normally the same in both clauses.

What you'll learn

• Choose -고 or -아/어서 for five test sentences and state the deciding rule in one sentence.
• Build both forms from verbs, including 오다, 앉다, 사다 and adjectives.
• Use the "there or with it" test to decide whether two actions are linked.
• Fix the most common errors: tense in the first clause and -고 used as a reason.

Before you start: you should know the polite ending -아요/-어요, because -아/어서 uses the same 아/어 form. If you want the full rules for each pattern first, read -고 and -아/어서.

What Is the Difference between -고 and -아/어서?

The difference is the link between the two parts. -고 treats the two parts as separate things that happen one after the other, or that are both true. -아/어서 treats them as connected: the first action leads into the second, and something from the first (a place, an object, a person) is still there in the second.

Two sentences show the contrast:

• 저는 아침을 먹고 학교에 가요. (jeoneun achimeul meokgo hakgyoe gayo.) = "I eat breakfast and go to school." The two actions are separate. Eating does not matter for going to school.
• 도서관에 가서 공부해요. (doseogwane gaseo gongbuhaeyo.) = "I go to the library and study (there)." The place of the first action is where the second one happens.

The word "and" fits both in English, but Korean sees different links. The next section turns the difference into a table.

-고 vs -아/어서: Side-by-Side Table

The table lists the points learners need most. Each row gives one answer for each pattern.

The table shows that the two patterns overlap in sequence but split on reasons and on how much the actions depend on each other. Each one gets a close look next.

When Do You Use -고?

Use -고 when you list actions in order or describe several facts about one thing. It is the simplest "and" in Korean. The pattern is verb stem + 고, and the stem never changes.

For separate actions in order. 어제 숙제를 하고 책을 읽었어요 (eoje sukjereul hago chaegeul ilgeosseoyo) = "Yesterday I did my homework and read a book." Tense is normally placed only on the last verb.

For listing. 저는 키가 크고 머리가 길어요 (jeoneun kiga keugo meoriga gireoyo) = "I am tall and my hair is long." Adjectives join with -고 in the same way. Using 커서 here would change the meaning to "I am tall, so ...".

For different subjects. The subjects of the two clauses can differ: 비가 오고 바람이 불어요 = "It rains and the wind blows."

With a command. -고 can end a clause before a command: 먹고 가세요 (meokgo gaseyo) = "Eat and then go."

To build the form, remove 다 from the dictionary form and add 고.

The form is easy to build, so the question is whether the actions are really separate. First, look at the second pattern.

When Do You Use -아/어서?

Use -아/어서 when the first action sets up the second one, and in the common case where the first action puts you somewhere or gives you something that the second action uses. It also gives a reason. The pattern is the 아/어 form of the verb + 서, the same 아/어 form that appears before 요 in the polite ending.

To carry a place, a person or an object forward. The key test is to add "there" or "with it" after the first verb:

• 도서관에 가서 공부해요 = "I go (to the library) and study (there)."
• 친구를 만나서 영화를 봤어요 (chingureul mannaseo yeonghwareul bwasseoyo) = "I met my friend and watched a movie (with him or her)."
• 시장에 가서 사과를 샀어요 (sijange gaseo sagwareul sasseoyo) = "I went to the market and bought apples (there)."

With sitting and standing verbs. The posture continues into the next action: 의자에 앉아서 기다리세요 (uijae anjaseo gidariseyo) = "Sit on the chair and wait." The word 앉아서 sounds like [안자서].

To give a reason. -아/어서 also means "because": 비가 와서 안 가요 (biga waseo an gayo) = "I'm not going because it rains." This reason meaning is covered in detail in the comparison of the two "because" patterns.

To build the form, take the 아/어 form of the verb and add 서:

The pattern is simple to build and subtle to choose, so the following example shows both patterns on the same verb.

Worked Example: 씻다 in Both Patterns

Follow the steps with "I wash my hands" and "I wash the fruit."

1. Start with the actions. 손을 씻다 (wash hands) then 밥을 먹다 (eat). Separately: 과일을 씻다 (wash the fruit) then 먹다 (eat it).
2. Ask whether the first action gives you something to use. Washing hands does not give you an object for eating. Washing the fruit does: the fruit is what you eat.
3. Choose the ending. For hands: 씻고. For the fruit: 씻어서.
4. Read the results. 손을 씻고 밥을 먹어요 = "I wash my hands and eat." 과일을 씻어서 먹어요 = "I wash the fruit and eat it."

You will know it worked when the second sentence has an "it" in English and the first does not. The most common slip is using -고 for both, which is acceptable in the second sentence but loses the link.

Can You Use Both in the Same Sentence?

You can use both in one sentence. They do different jobs, so they combine easily. A natural example: 아침에 일어나서 세수하고 밥을 먹어요 (achime ireonaseo sesuhago babeul meogeoyo) = "In the morning I get up, wash my face and eat."

Here 일어나서 links getting up to the washing that follows, and 세수하고 then lists the next step. The pattern can go on: 일어나서 세수하고 밥을 먹고 학교에 가요.

Also, many sequences work with either ending. 친구를 만나고 영화를 봤어요 and 친구를 만나서 영화를 봤어요 are both heard. The first just lists two events. The second suggests that the movie was with the friend.

The overlap is real, so a short rule helps you choose.

Which One Should You Pick? a Simple Rule of Thumb

Use the "there or with it" test. Use this four-step check.

1. Find the two parts. Say them in English: "go to the library, study."
2. Add "there" or "with it." Does the second action happen in the place or with the thing from the first? If yes, use -아/어서.
3. Check for a reason. If the first part explains why the second one happens, use -아/어서. If it only adds another fact, use -고.
4. Otherwise use -고. For separate actions or a list, -고 is the right choice.

Apply the check to "I eat breakfast and go to school." Eating does not carry anything into school, so use 먹고. Apply it to "I buy coffee and drink it." The coffee carries over, so use 커피를 사서 마셔요.

If you cannot decide between a sequence and a reason, -고 is the safer choice for a plain sequence, because it never claims a reason. The next section looks at the places where learners slip.

What Mistakes Do Learners Make with These Two?

Learners most often use the wrong one for a reason, or add tense to -아/어서. Four mistakes appear again and again.

1. Using -고 for a reason. 비가 오고 안 가요 does not mean "I'm not going because of the rain." Say 비가 와서 안 가요.
2. Adding tense to -아/어서. *어제 학교에 갔어서 공부했어요 is wrong. Say 어제 학교에 가서 공부했어요. The past tense goes on the last verb.
3. Using -아/어서 with a different subject. For the "and then" meaning the two clauses share a subject. 동생이 와서 제가 갔어요 changes the meaning. For different subjects, use -고: 동생이 오고 제가 갔어요.
4. Following a reason clause with a command. *비가 와서 우산을 가져가세요 is wrong. Use -(으)니까: 비가 오니까 우산을 가져가세요.

Use this checklist when a sentence feels wrong: Is there a reason? Does the second action use something from the first? Is there a tense marker on 서? The remaining differences are edge cases.

When Do the Two Patterns Work Differently?

The two patterns work differently with adjectives, with verbs of motion and with the negative.

• Adjectives. With adjectives, -고 lists qualities (싸고 맛있어요, "cheap and tasty"), while -아/어서 gives a reason (싸서 많이 샀어요, "it was cheap, so I bought a lot").
• Verbs of motion and posture. 가다, 오다, 앉다, 서다 (to stand) and 만나다 almost always take -아/어서 when the next action happens there or with them.
• Negatives. Both patterns take the negative of the verb: 안 먹고 가요 (go without eating) and 못 가서 죄송해요 (I'm sorry I couldn't go).
• One honest limit. This page compares the "and" and "and then" meanings of the two patterns. The pure reason meaning of -아/어서 and its contrast with -기 때문에 are covered in separate lessons, and so are other "and" patterns such as -(으)면서.

Since the choice depends on the link between the actions, practice is the quickest way to feel it.

Practice: Choose the Right Pattern

Try the five items before you read the answer key.

1. Choose. "I go to the library and study (there)." Which fits: 도서관에 가고 공부해요 or 도서관에 가서 공부해요?
2. Choose. "I eat breakfast and go to school." Which is better, 먹고 or 먹어서?
3. Fix the error. A learner says 어제 친구를 만났어서 영화를 봤어요. What should change?
4. Build. Make the -고 form and the -아/어서 form for 사다.
5. Translate. "I'm not going because it rains." Use 오다.

Answer key

1. 도서관에 가서 공부해요. The place carries over to the second action.
2. 먹고. The two actions are separate.
3. 친구를 만나서 영화를 봤어요. Remove the tense from the first clause and put it on the last verb.
4. 사고 and 사서.
5. 비가 와서 안 가요. Only -아/어서 gives the reason.

A final test: if you can add "there" or "with it" after the first verb, use -아/어서. If the two actions are separate or the sentence is a list, use -고.

What Should You Learn Next?

After this comparison, study each pattern on its own and then compare related ones. This page compares the two patterns but does not teach every use of either one.

1. Read the full lesson on -고, which covers listing, sequence and the tense rule.
2. Read the full lesson on -아/어서, which covers both the reason and the sequence meanings.
3. See how another "and" differs in -(으)면서 vs -고.
4. Check the beginner list at Beginner Grammar to see where both patterns sit among the A2 lessons.
5. Compare other confusing pairs at Confusing Grammar Compared.

With these steps, the choice between -고 and -아/어서 becomes automatic: ask how tightly the actions are linked, then add the matching ending.

Frequently Asked Questions

What is the difference between -고 and -아/어서?

-고 joins separate actions or facts: 아침을 먹고 학교에 가요. -아/어서 joins actions that depend on each other, or gives a reason: 도서관에 가서 공부해요 means you study at the library. In the second sentence something from the first action, here the place, carries into the second.

Can I always replace -고 with -아/어서?

No. -아/어서 changes the meaning to a linked sequence or a reason. 손을 씻고 먹어요 means you wash your hands and eat, but 손을 씻어서 먹어요 can sound as if the hands are what you eat. It also does not list adjectives the way -고 does: 크고 lists a quality, while 커서 gives a reason.

Which one sounds more natural in speech?

Both are everyday patterns. -고 is the usual way to chain separate actions and to list qualities. -아/어서 is the natural choice after verbs such as 가다, 오다, 앉다, 사다 and 만나다 when the next action happens there. Speakers choose by meaning, not by formality.

Which one appears more often on TOPIK?

No reliable count is available, so this site makes no claim. Both patterns appear in elementary reading and grammar items. Test items often hinge on tense in the first clause and on whether the sentence needs a reason, so check those two points first.

What is the quickest rule to remember?

Add "there" or "with it" after the first verb. If it fits, the actions are linked, so use -아/어서. If the actions are separate or you are listing, use -고. Also remember that only -아/어서 can mean "because," and it never takes a tense marker.

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