In short

To say you go somewhere in order to do something, attach -(으)러 to the verb stem and follow it with a motion verb - 가다, 오다, 다니다, 나가다: 밥 먹으러 가요 (bap meogeureo gayo, I’m going to eat). For a purpose with any verb, or to say you intend / are about to do something, use -(으)려고 (+ 하다): 사려고 돈을 모아요 (saryeogo doneul moayo, I’m saving money to buy it).

The rule

Step 1 - -(으)러 = “go/come to do X”, and it needs a motion verb

-(으)러 marks the goal of a trip. The one hard restriction: the main clause verb must be a verb of motion - 가다 (go), 오다 (come), 다니다 (attend / go regularly), 나가다 (go out). You literally go/come in order to do the -(으)러 action.

Verb stem + -(으)러 + 가다/오다/다니다/나가다

• 밥 먹으러 가요. (bap meogeureo gayo) - (I) go to eat.
• 친구를 만나러 왔어요. (chingureul mannareo wasseoyo) - (I) came to meet a friend.

Step 2 - The allomorph, and the ㄹ-stem twist

The (으) is the usual 받침-driven choice:

• stem ends in a vowel -> -러: 사다 -> 사러 (sareo, to buy)
• stem ends in a 받침 -> -으러: 먹다 -> 먹으러 (meogeureo, to eat)
• a ㄹ-stem keeps its ㄹ and takes the bare -러 (no 으): 놀다 -> 놀러 (nolleo, to play), 만들다 -> 만들러 (mandeulleo, to make)

Note the contrast with -(으)세요 (lesson 21): there the ㄹ drops (살다 -> 사세요), but before 러 it stays (살다 -> 살러, salleo). The 으-inserting form triggers irregular stems as always (lesson 17): 듣다 (ㄷ-irregular) -> 들으러 (deureureo, to listen), not *듣으러.

Step 3 - -(으)러 accepts any mood in the main clause

Because the trip itself can be stated, ordered, or proposed, the main motion verb may be a statement, a command, or a suggestion:

• 놀러 갈까요? (nolleo galkkayo?) - Shall we go out to have fun? (suggestion)
• 밥 먹으러 가세요. (bap meogeureo gaseyo) - Please go eat. (command)

Step 4 - -(으)려고 = “intending to”, with any verb

-(으)려고 also marks purpose, but it is about the doer’s intention, so the main clause verb is free - it need not be a motion verb:

Verb stem + -(으)려고 + (any verb) -> 집을 사려고 돈을 모아요. (jibeul saryeogo doneul moayo) - (I’m) saving money to buy a house.

The allomorph works exactly like -(으)러: vowel -> -려고 (가다 -> 가려고, garyeogo), 받침 -> -으려고 (먹다 -> 먹으려고, meogeuryeogo), ㄹ-stem keeps ㄹ -> -려고 (만들다 -> 만들려고, mandeullyeogo). Two limits go with it:

• Same subject. The person who intends and the person who does the main action must be one and the same. For a purpose across two different subjects Korean uses -도록 (lesson 51).
• No command or suggestion in the main clause. -(으)려고 states a plan, so the main verb must be a plain statement - never an imperative or a propositive. Want let’s or please? Switch to -(으)러 (Step 3).

Step 5 - -(으)려고 하다 = intend / be about to

Add 하다 to make a full predicate meaning plan to or, on the verge of something, be about to:

• 내일 일찍 일어나려고 해요. (naeil iljjik ireonaryeogo haeyo) - (I) intend to get up early tomorrow. (intention)
• 비가 오려고 해요. (biga oryeogo haeyo) - It’s about to rain. (imminent - here the subject is not a willing person, so only the “about to” reading survives; a subject who can intend keeps the intention reading whoever they are, third person included - 친구가 이번 학기에 기타를 배우려고 해요 (chinguga ibeon hakgie gitareul baeuryeogo haeyo, my friend intends to learn the guitar this term) - unlike -고 싶다 (lesson 26), which has to become -고 싶어 하다 for a third person)

Step 6 - Choosing, and negative purpose

Use -(으)러 the moment the sentence is someone going/coming somewhere; use -(으)려고 for a purpose behind any other action, or for intention. Only -(으)려고 builds a negative purpose (so as not to…), with 안 or -지 않으려고: 늦지 않으려고 뛰어요 (neutji aneuryeogo ttwieoyo, (I) run so as not to be late). The heavier written purpose forms -기 위해서 and -도록, and the conditional -(으)려면, all wait for lesson 51.

Forms & patterns

-(으)러 - the allomorph table (main verb 가다):

-(으)려고 - the allomorph table (+ 하다):

-(으)러 vs -(으)려고 - the contrast:

Examples

Common mistakes

• 책을 사러 돈을 모아요. (Chaegeul sareo doneul moayo.) -> 책을 사려고 돈을 모아요. (Chaegeul saryeogo doneul moayo.) - -(으)러 works only when the main verb is a motion verb (가다/오다/다니다/나가다). With 모으다 (save up) the purpose ending must be -(으)려고.
• 밥 먹러 가요. (Bap meongneo gayo.) -> 밥 먹으러 가요. (Bap meogeureo gayo.) - After a 받침 the ending is -으러, not a bare -러. The 으 is the same vowel you insert everywhere after a consonant.
• 밥 먹으려고 갑시다. (Bap meogeuryeogo gapsida.) -> 밥 먹으러 갑시다. (Bap meogeureo gapsida.) - A let’s (or a command) main clause cannot follow -(으)려고. A suggestion of a trip takes -(으)러.
• 놀으러 가요. (Noreureo gayo.) -> 놀러 가요. (Nolleo gayo.) - A ㄹ-stem keeps its ㄹ and adds the bare -러; it never inserts 으. Same for 만들다 -> 만들러.
• 갈려고 해요. (Gallyeogo haeyo.) -> 가려고 해요. (Garyeogo haeyo.) - 가다 is a vowel-final stem, so it takes -려고 directly. There is no extra ㄹ; *갈려고 is a common slip.

Tips

• Trip? -(으)러. Anything else? -(으)려고. If the sentence is someone going/coming somewhere, reach for -(으)러 - it can only ride on 가다/오다/다니다/나가다. For a purpose behind any other action, or for intention, use -(으)려고.
• -(으)려고 will not take orders. You can say 놀러 가자 or 먹으러 가세요, but *놀려고 가자 and *먹으려고 가세요 are wrong: -(으)려고 reports a plan, so its main clause is always a plain statement.
• The ㄹ stays here. Unlike -(으)세요 (사세요, 만드세요), ㄹ-stems keep the ㄹ before 러 and 려고: 놀러, 만들러, 만들려고. Insert no 으.
• -(으)려고 하다 also means “on the verge of.” With weather or an involuntary event it drops the intend sense and just means about to: 비가 오려고 해요 (it’s about to rain), 버스가 떠나려고 해요 (the bus is about to leave).