Used with the verb '하다' to express the purpose of an action.
When to use
Purpose with 하다, Explaining plans, Intention of action
The nuance
Attaches only to the verb '하다' to indicate purpose; not used with other verbs.
하러 (ha-reo, hareo) · 으러 (eu-reo, eureo)
'하러' and '으러' both express purpose, but '하러' combines specifically with the verb '하다', while '으러' attaches to verb stems to clearly indicate purpose.

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Used with the verb '하다' to express the purpose of an action.
When to use
Purpose with 하다, Explaining plans, Intention of action
The nuance
Attaches only to the verb '하다' to indicate purpose; not used with other verbs.
Attaches to verb stems to express the purpose of an action.
When to use
Expressing purpose, Everyday conversation, Action plans
The nuance
Attaches to verb stems without vowel changes to indicate purpose; can be used with all verbs except '하다' which uses '하러'.
학교에 공부하러 갔어요.
hak-gyo-e gong-bu-ha-reo gass-eo-yo., hak gyo e gong bu ha reo gass eo yo.
Correct because it combines with the verb '하다' to indicate purpose.
학교에 공부으러 갔어요.
hak-gyo-e gong-bu-eu-reo gass-eo-yo., hak gyo e gong bu eu reo gass eo yo.
Incorrect because '공부' is a noun and must use '하러' with '하다'; '공부으러' is wrong.
친구를 만나러 카페에 갔어요.
chin-gu-reul man-na-reo ka-pe-e gass-eo-yo., chin gu reul man na reo ka pe e gass eo yo.
Correct because '러' attaches to the verb stem '만나' to indicate purpose.
친구를 만나하러 카페에 갔어요.
chin-gu-reul man-na-ha-reo ka-pe-e gass-eo-yo., chin gu reul man na ha reo ka pe e gass eo yo.
'만나다' is not '하다', so '하러' cannot be used here.
운동하러 공원에 갑니다.
un-dong-ha-reo gong-won-e gap-ni-da., un dong ha reo gong won e gap ni da.
Appropriate because it combines with '운동하다' to express purpose.
운동으러 공원에 갑니다.
un-dong-eu-reo gong-won-e gap-ni-da., un dong eu reo gong won e gap ni da.
Incorrect because '운동' is a noun and must use '하러' with '하다'.
편지를 보내러 우체국에 갔어요.
pyeon-ji-reul bo-nae-reo u-che-guk-e gass-eo-yo., pyeon ji reul bo nae reo u che guk e gass eo yo.
Correct as '러' attaches to the verb stem '보내' to indicate purpose.
편지를 보내하러 우체국에 갔어요.
pyeon-ji-reul bo-nae-ha-reo u-che-guk-e gass-eo-yo., pyeon ji reul bo nae ha reo u che guk e gass eo yo.
'보내다' is not '하다', so '하러' cannot be used here.
Which sentence correctly uses '하러'?
Which sentence requires '으러'?
Which sentence is incorrect?