In short

A Korean adjective is not a word you attach “to be” to - it is the verb. 예쁘다 (yeppeuda) means to be pretty, and it conjugates with the same 아/어 engine as 가다: 예뻐요 (yeppeoyo) - it’s pretty. Never add the copula: *예쁜이에요 is the single most common beginner error in the language.

The rule

Step 1 - Korean has no “be + adjective”

English builds descriptions out of two words: is plus pretty. Korean builds them out of one. 형용사 (hyeongyongsa, descriptive verb) is a class of verbs, listed in the dictionary in the same -다 form as action verbs, and conjugated by the same machinery you learned in lesson 10.

So the sentence the weather is good is 날씨가 좋아요. (Nalssiga joayo.) - subject, then the predicate, and nothing else. There is no slot for 이에요/예요 and nothing is missing.

Step 2 - Three predicate classes, plus a hybrid

Every Korean sentence ends in one of these:

• Noun + 이다 - identity. 학생이에요. (Haksaengieyo.) - I’m a student. See lesson 2.
• 동사 (dongsa, action verb) - what someone does. 먹어요. (Meogeoyo.) - (I) eat.
• 형용사 (hyeongyongsa, descriptive verb) - what someone or something is like. 좋아요. (Joayo.) - It’s good.

The fourth, hybrid class is 있다 / 없다. They describe a state like adjectives and conjugate like them, but their modifier form follows the verbs (see Step 6). All the 있다-compounds inherit this: 맛있다, 재미있다, 재미없다.

The practical consequence: only the first class takes 이다. If your predicate is a 형용사, adding 이에요 is like saying it is is-pretty.

Step 3 - Conjugating one is nothing new

Take the dictionary form, strip -다, and apply the 아/어 rule: stem-final ㅏ or ㅗ takes -아요, everything else takes -어요, and 하다 stems take 해요.

• 좋 + 아요 -> 좋아요 (joayo) - it’s good
• 맛있 + 어요 -> 맛있어요 (masisseoyo) - it’s delicious
• 크 + 어요 -> 커요 (keoyo) - it’s big (으-elision, the same contraction as 쓰다 -> 써요)
• 조용하 + 여요 -> 조용해요 (joyonghaeyo) - it’s quiet

Irregular stems behave exactly as they do for action verbs: ㅂ-irregular 덥다 -> 더워요 (deowoyo), but regular 좁다 -> 좁아요 (jobayo). The past tense, 합쇼체, -(으)면 and the rest all attach identically.

Step 4 - What adjectives cannot do

Because they describe a state rather than an action, 형용사 refuse the endings that presuppose doing something:

• -고 있다 (in progress) - a state is not in progress. *좋고 있어요 is impossible; just say 좋아요.
• -고 싶다 (want to) - you cannot want to be tall directly. Use -아/어지다 (become) first: 예뻐지고 싶어요. (Yeppeojigo sipeoyo.) - I want to become pretty.
• -(으)러 (go in order to) - takes an action only. *바쁘러 가요 is impossible.
• Imperatives and propositives - you cannot order someone into a quality. *예쁘세요! as a command and *바쁩시다! (bappeupsida) are both out. Note the trap: 예쁘세요 as a statement is perfectly good - it is honorific description, you are pretty - so the block is on the command reading, not on the shape.

If a pattern works with 형용사, it works because it is state-friendly: -(으)면, -지만, -아/어서, the past -았/었-, and 안-negation all attach freely.

Step 5 - Making a verb out of an adjective: -아/어하다

To turn a description into an action - what a person does about a quality - take the 아/어 form and add 하다:

Adjective 아/어 form + 하다

좋아 + 하다 -> 좋아하다 (joahada, to like), 싫어 + 하다 -> 싫어하다 (sireohada, to dislike), 예뻐 + 하다 -> 예뻐하다 (yeppeohada, to dote on).

This changes the particles. The adjective 좋다 describes the thing, so the thing is the subject with 이/가; the verb 좋아하다 acts on it, so the thing is the object with 을/를:

• 김치가 좋아요. (Gimchiga joayo.) - I like kimchi (literally kimchi is good/pleasing).
• 김치를 좋아해요. (Gimchireul joahaeyo.) - I like kimchi.

The -아/어하다 form is also how you report someone else’s feelings, which is why 좋아하다 is the normal verb for third persons.

Step 6 - 안 + 형용사, and a preview of the modifier split

Negation is simple: put 안 in front, with a space. 안 좋아요 (an joayo), 안 비싸요 (an bissayo). One catch for 하다-adjectives: unlike 하다-verbs, they are single words, so 안 goes before the whole thing - 안 조용해요 (an joyonghaeyo), never *조용 안 해요. Full treatment in lesson 14.

Finally, file this away: when a predicate is put in front of a noun to modify it, the class decides the ending - 동사 takes -는 (먹는 meongneun) and 형용사 takes -(으)ㄴ (예쁜 yeppeun, 좋은 joeun). This is the main reason knowing the class matters; it is taught in full in lesson 24.

Forms & patterns

The predicate classes side by side:

A real adjective paradigm - identical machinery to the action verbs:

Note the last row: 맛있다 is a descriptive verb, but because it is built on 있다 its modifier is -는, not -(으)ㄴ.

The blocked patterns:

형용사 + -아/어하다 -> 동사:

Examples

Common mistakes

• 가방이 예쁜이에요. (Gabangi yeppeunieyo.) -> 가방이 예뻐요. (Gabangi yeppeoyo.) - 예쁘다 is already a verb. Adding 이에요 duplicates the predicate; conjugate the adjective instead.
• 크어요. (Keueoyo.) -> 커요. (Keoyo.) - the 으 of the stem drops before -어요. The contraction is obligatory, exactly as in 쓰다 -> 써요.
• 저는 커피를 좋아요. (Jeoneun keopireul joayo.) -> 저는 커피를 좋아해요. (Jeoneun keopireul joahaeyo.) - 좋다 is descriptive and takes 이/가 (커피가 좋아요); with the object particle 을/를 you need the derived verb 좋아하다.
• 날씨가 좋고 있어요. (Nalssiga joko isseoyo.) -> 날씨가 좋아요. (Nalssiga joayo.) - -고 있다 marks an action in progress, and a quality is not an action. The plain form already means is good right now.
• 방이 조용 안 해요. (Bangi joyong an haeyo.) -> 방이 안 조용해요. (Bangi an joyonghaeyo.) - 조용하다 is one word, unlike the 하다-verbs that split (공부 안 해요), so 안 goes in front of the whole adjective.

Tips

• Read the dictionary form as an English sentence, not an English word. Learn 크다 as to be big, not as big. Do that from day one and *큰이에요 never forms in your head.
• A one-question class test. Can you say it with -고 있다, or command it? Then it is a 동사. If both feel wrong, it is a 형용사 - and it will take -(으)ㄴ in front of a noun.
• 좋다 vs 좋아하다 is about who owns the feeling. 좋다 presents the thing as pleasing (김치가 좋아요), 좋아하다 presents you as liking it (김치를 좋아해요). About a third person, the -아/어하다 verb is the natural choice.
• Watch the 있다-family. 맛있다, 재미있다, 재미없다 are descriptive in meaning but take -는 as their modifier: 맛있는 음식 (masinneun eumsik) - tasty food, never *맛있은.