Connecting Sentences · -고, -지만, -아서/어서

4. Common mistakes

❌ Mistake 1 — Past tense inside -아서/어서

✖ 어제 바빴어서 못 갔어요.
✔ 어제 바빠서 못 갔어요.
  eo-je ba-ppa-seo mot ga-sseo-yo.

With 아서/어서, the tense goes only on the last verb. Here 갔어요 already puts the sentence in the past. The same applies to 피곤했어서, so say 피곤해서.

❌ Mistake 2 — -고 when you mean "but"

✖ 이 가방은 예쁘고 비싸요.
✔ 이 가방은 예쁘지만 비싸요.
  i ga-bang-eun ye-ppeu-ji-man bi-ssa-yo.

The first sentence is grammatical, but it means "pretty and expensive". It is wrong for the meaning "pretty, but expensive". Use 지만 when the second part goes against what you expect.

❌ Mistake 3 — -지만 for two actions in order

✖ 아침을 먹지만 학교에 가요.
✔ 아침을 먹고 학교에 가요.
  a-chi-meul meok-go hak-gyo-e ga-yo.

지만 means "but", so the first sentence says "I eat breakfast, but I go to school". That is not what you want to say. Two actions in order use 고, which means "and then".

❌ Mistake 4 — A command after -아서/어서

✖ 비가 와서 우산을 가져가세요.
✔ 비가 오니까 우산을 가져가세요.
  bi-ga o-ni-kka u-sa-neul ga-jyeo-ga-se-yo.

아서/어서 cannot be followed by a command or a suggestion, such as 하세요 or 해요 as a suggestion. When you ask the listener to act, use 니까 instead. It also means "because", but it allows commands.

❌ Mistake 5 — The wrong vowel in the ending

✖ 먹아서 / 피곤하어서
✔ 먹어서 / 피곤해서
  meo-geo-seo / pi-gon-hae-seo

먹다 ends in ㅓ, which is not ㅏ or ㅗ, so it takes 어서. 하다 verbs always become 해서, never 하어서. Check the last vowel of the stem before you choose.