In short

To say what you want to do, add -고 싶다 to a verb stem and conjugate 싶다 like an adjective: 가다 -> 가고 싶어요 (gago sipeoyo, I want to go). To propose doing something together, add -(으)ㄹ까요?: 커피 마실까요? (keopi masilkkayo?, Shall we have coffee?). One catch to remember from the start: -고 싶다 speaks only for you or the person you are asking - a third person’s wish needs -고 싶어 하다.

The rule

Step 1 - -고 싶다 = verb stem + -고 싶다, and 싶다 inflects as an adjective

The desire pattern is built on the connective -고 from lesson 23 plus the auxiliary 싶다 (sipda, to want to):

Verb stem + -고 싶다

싶다 carries no tense or politeness by itself; it is a 보조 형용사 (auxiliary adjective), so it conjugates with the same machinery as any 형용사 from lesson 11. 싶 has the stem vowel ㅣ (not ㅏ or ㅗ), so the 아/어 form takes 어: 싶 + 어요 -> 싶어요 (sipeoyo). That gives 가고 싶어요 (I want to go), past 가고 싶었어요 (gago sipeosseoyo, I wanted to go), and the modifier 먹고 싶은 것 (meokgo sipeun geot, the thing I want to eat) - present modifier -은, because 싶다 is an adjective, never the verb -는.

Step 2 - Person matters: -고 싶다 (I / you) vs -고 싶어 하다 (someone else)

-고 싶다 reports a feeling from the inside, so in a statement it is about the speaker, and in a question it naturally asks the listener. To speak of a third person’s wish - something you only observe from outside - Korean turns the feeling into behaviour with -어 하다:

Third person: Verb stem + -고 싶어 하다 -> 가고 싶어 해요 (gago sipeo haeyo, he/she wants to go)

싶어 하다 conjugates as a regular action verb (하다 verb): 싶어 해요, 싶어 했어요.

Step 3 - Only action verbs take -고 싶다

-고 싶다 attaches to action verbs only, never to an adjective. You cannot say *예쁘고 싶다 for want to be pretty. Turn the adjective into a change-of-state verb with -아/어지다 (lesson 37) first: 예쁘다 -> 예뻐지다 -> 예뻐지고 싶어요 (yeppeojigo sipeoyo, I want to become pretty).

Step 4 - The object may take 을/를 or 이/가

Because 싶다 is adjective-like, the object of the wanted verb can keep its normal 을/를, or switch to 이/가 to spotlight it as the thing desired. Both are correct:

물을 마시고 싶어요 (mureul masigo sipeoyo) = 물이 마시고 싶어요 (muri masigo sipeoyo) - I want to drink water.

을/를 is the neutral, everyday choice; 이/가 leans on water specifically. With 3rd-person -고 싶어 하다, stay with 을/를: 동생이 물을 마시고 싶어 해요.

Step 5 - Negation: two spots

Put 안 before the main verb, or attach the long -지 않다 to 싶다 - both are used:

• 안 가고 싶어요 (an gago sipeoyo) - I don’t want to go.
• 가고 싶지 않아요 (gago sipji anayo) - I don’t want to go. (long form, negating 싶다)

Step 6 - Proposing with -(으)ㄹ까요?

-(으)ㄹ까요? floats a proposal and asks the other person’s willingness. Same ending, two readings by context: 제안 shall WE? (with 우리/같이) and 의향 shall I? (with 저/제가):

• 우리 갈까요? (uri galkkayo?) - Shall we go?
• 제가 할까요? (jega halkkayo?) - Shall I do it?

The (으) is chosen by the 받침, exactly like every -(으)ㄹ ending - see the table below.

Step 7 - The everyday alternatives, and what is deferred

A plain 같이 + -아/어요 statement is an equally common, warmer let’s: 같이 가요 (gachi gayo, let’s go together). 우리 + verb does the same inclusive job: 우리 밥 먹어요 (uri bap meogeoyo, let’s eat). Typical replies are 좋아요 (joayo, sounds good) or 그래요 (geuraeyo, okay, sure). Two more let’s forms belong to later registers - the formal -(으)ㅂ시다 (lesson 27) and the casual -자 (lesson 44) - and the softer I wish / I’d like -(으)면 좋겠다 is lesson 61.

Forms & patterns

싶다 conjugates as an adjective (paradigm on 가다 -> 가고 싶다):

-(으)ㄹ까요? - the allomorph is chosen by the 받침:

Ways to propose “let’s / shall we”, from everyday to deferred:

Examples

Common mistakes

• 동생이 가고 싶어요. (Dongsaengi gago sipeoyo.) -> 동생이 가고 싶어 해요. (Dongsaengi gago sipeo haeyo.) - -고 싶다 states only your own or your listener’s wish. A third person’s desire, seen from outside, needs -고 싶어 하다.
• 예쁘고 싶어요. (Yeppeugo sipeoyo.) -> 예뻐지고 싶어요. (Yeppeojigo sipeoyo.) - -고 싶다 takes action verbs only. To want to be an adjective, make it become first with -아/어지다.
• 먹고 싶는 것 (meokgo simneun geot) -> 먹고 싶은 것 (meokgo sipeun geot) - 싶다 conjugates as an adjective, so its present modifier is -은, never the verb -는.
• 만들을까요? (mandeureulkkayo?) -> 만들까요? (mandeulkkayo?) - a ㄹ-stem already ends in ㄹ, so it adds no 을; the stem’s own ㄹ is the -(으)ㄹ of the ending.
• 가고싶어요. (gagosipeoyo.) -> 가고 싶어요. (gago sipeoyo.) - 싶다 is a separate auxiliary word: keep a space after -고. Endings glue on with no space, but auxiliaries take one.

Tips

• 싶다 feels; 하다 shows. -고 싶다 is the wish felt from inside (yours, or the listener’s when you ask); -고 싶어 해요 is the wanting you observe in someone else. English want hides this split, so it is the error learners make longest.
• -(으)ㄹ까요? asks, 같이 -아/어요 tells. 갈까요? checks whether the other person is willing (shall we?); 같이 가요 is a warm, settled let’s go. Both are plain 해요체 and both are everyday - reach for the formal 갑시다 or casual 가자 only when the whole conversation is in that register.
• Answer a 마실까요? with a set phrase. 좋아요 (sounds good) and 그래요 (sure) accept; 다음에요 (daeumeyo, next time) or 아니요, 괜찮아요 (aniyo, gwaenchanayo, no, I’m fine) decline gently. You will hear these far more than any textbook grammar.
• Object case is a free choice, not a rule you can get wrong. 물을 마시고 싶어요 and 물이 마시고 싶어요 are both fine; default to 을/를 and treat 이/가 as light emphasis on the thing you crave.