Recall that an adverb is usually used to modify a verb, just as an adjective is usually used to modify a noun. In English, in general, you add “ly” to change adjectives to adverbs. For example, aggressive is an adjective and aggressively is an adverb. In Japanese, there is also a regular way to change adjectives to adverbs, as follows:

い-adjective: change い to く

な-adjective: change な to に

Exception: change いい (good) to よく (well).

Examples

早い （はやい）is an い-adjective which means early. When it is used as an adverb, change い to く and it becomes 早く.

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Unlike English, which you may put adverb either before or after the main verb in a sentence, you usually put the Japanese adverb before the main verb.

静か （しずか）is a な-adjective which means quiet. When it is an adverb, it becomes 静かに.

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Conjugation is to modify of a verb or an adjective in order to fulfil a change in tense or to supplement additional meanings.

All Korean conjugation for verbs and adjectives are under one of the following 3 categories:

1. 고-type: Original Stem + Suffix
2. 으-type: Alternate Stem + (으) + Suffix
3. 어-type: Alternate Stem + 어/아 + Suffix, Vowel Contractions

The basic idea is to identify the word stem and attach a suffix to the stem.

1. 고-type Conjugation

This is named after the basic 하고 conjugation. Original stem is always used, with the following exceptions:

• For ㄹ-irregular, when the attaching suffix starts with ㄴ, ㅅ or ㅂ (e.g. 는, 네, 습니다), alternate stem is used (i.e. ㄹ is dropped).
• For ㅎ-irregular, use alternate stem when the attaching suffix is 네.

Examples

Plain Form	Meaning	Stem 1	Stem 2	+고	+습/ㅂ니다	+네	Remarks
하다	do	하	하	하고	하습니다	하네
먹다	eat	먹	먹	먹고	먹습니다	먹네
알다	know	알	아	알고	압니다	아네	ㄹ-irregular
그렇다	to be so	그렇	그러	그렇고	그렇습니다	그러네	ㅎ-irregular

Note: Original Stem = Stem 1, Alternate Stem = Stem 2.

2. 으-type Conjugation

Use alternate stem and if the stem ends with a consonant, insert 으 after the stem.

However, there are 3 exceptions:

• For ㅅ-irregular, 으 is always inserted.
• For ㄹ-irregular, if the suffix starts with 면 or 러, use original stem and do not insert 으.
• For 르-irregular, use original stem instead.

Examples

Plain Form	Meaning	Stem 1	Stem 2	+ (으)세요	+ (으)면	+ (으)러	Remarks
하다	do	하	하	하세요	하면	하러
먹다	eat	먹	먹	먹으세요	먹으면	먹으러
알다	know	알	아	아세요	알면	알러	ㄹ-irregular
짓다	build	짓	지	지으세요	지으면	지으러	ㅅ-irregular
고르다	choose	고르		고르세요	고르면	고르러	르-irregular

3. 어-type Conjugation

You can consider 어-type conjugation as a 2-step process. First you need to determine whether 아 or 어 should be attached, then you need to do a vowel contraction if necessary.

Use alternate stem as word stem for all 어-type conjugation, except that for ㄹ-irregular, use original stem instead.*

The following rules determine whether to attach 어 or 아 before the suffix:

1. If the last vowel of the stem is a 오 or 아, attach 아 + suffix.
2. If the last vowel is 으 and its previous hangul has a 오/아 vowel, attach 아 + suffix.
3. Otherwise, attach 어 + suffix.

Next, if the stem has no ending consonant, contract the last vowel of the stem and the added 아/어 as shown in the table below. Pay special attention to 하다-related verbs and adjectives, and ㅅ-irregular, as they are the exceptions.*

Case	Contraction	Example	Meaning	Stem + 아/어요	Remarks
*	하 +아 → 해	공부하다	study	공부하 + 아요 → 공부해요	하다-related
1	아 +아 → 아	가다	go	가 +아요 → 가요
	오 +아 → 와	오다	come	오 +아요 → 와요
		돕다	help	도오 +아요 → 도와요	ㅂ-irregular
2	으 +아 → 아	바쁘다	busy	바쁘 +아요 → 바빠요	으-irregular
		고르다	choose	골르 +아요 → 골라요	르-irregular
3	우 +어 → 워	배우다	learn	배우 +어요 → 배워요
		춥다	cold	추우 +어요 → 추워요	ㅂ-irregular
	으 +어 → 어	쓰다	write	쓰 +어요 → 써요	으-irregular
		부르다	call	불르 +어요 → 불러요	르-irregular
	이 +어 → 여	치다	hit	치 +어요 → 쳐요
	어 +어 → 어 or 애	건너다	go over	건너 +어요 → 건너요
		그렇다	to be so	그러 +어요 → 그래요	ㅎ-irregular
	외 +어 → 왜	되다	become	되 +어요 → 돼요
	애 +어 → 애	지내다	spend time	지내 +어요 → 지내요
	여 +어 → 여	펴다	unfold	펴 +어요 → 펴요
All	No Contraction	먹다	eat	먹 +어요 → 먹어요
		듣다	listen	들 +어요 → 들어요	ㄷ-irregular
		놀다	play	놀 +아요 → 놀아요	ㄹ-irregular*
		낫다	get better	나 +아요 → 나아요	ㅅ-irregular*

Use original stem for ㄹ-irregular, and never do vowel contractions forㅅ-irregular.

We know a regular verb in English may be modified to its past tense form by adding suffix ed to it, and English adjectives use verb to be (e.g. was) to represent past tense.

In Korean, however, adjectives are verb-like in grammatical constructions, and both verbs and adjectives follow a similar set of rules to conjugate to their modified forms.

Korean verbs and adjectives are mostly regular, meaning that they follow a simple rule to conjugate. For the remaining irregular verbs and adjectives, the good news is, they are not as “irregular” as English verbs. There is one set of conjugation rules for each group of irregular verbs and adjectives.

Word stem is the basic unit to conjugate. Regular verb or adjective only has an original stem for conjugation. Irregular verb or adjective has an additional alternate stem, as explained in the section below.

Original Stems of Korean Verbs and Adjectives

When a Korean verb or adjective is in plain form (the form you can look up from a dictionary), it always ends with 다.

It is then easy to identify the original stem:

Get the original stem of any verb or adjective by removing the last hangul 다 of the plain form of the word.

Alternate Stems of Korean Verbs and Adjectives

You will need to know what kind of irregular verb/adjective it is, before identifying its alternate stem.

Verbs/Adjectives	Alternate Stem Formation from Original Stem
Regular	Keep the original stem unchanged
ㅂ-Irregular	Drop final consonant ㅂ, add hangul 우**
ㅅ-Irregular	Drop final consonant ㅅ
ㄷ-Irregular	Replace final consonant ㄷ with ㄹ
ㅎ-Irregular	Drop final consonant ㅎ
ㄹ-Irregular	Drop final consonant ㄹ
으-Irregular	Keep the original stem unchanged
르-Irregular	Add ㄹ as an ending consonant to the second to last hangul

** There is an additional alternate stem for 2 ㅂ-irregular words for 어-type conjugation: 돕다 (to help) and 곱다 (to be pretty), by replacing the final consonant ㅂ with hangul 오.

Examples

Verbs/Adjectives	Dictionary Form	Meaning	Original Stem	Alternate Stem
Regular	먹다	eat	먹	먹
ㅂ-Irregular	춥다	cold	춥	추우
	돕다	help	돕	도우 or 도오
ㅅ-Irregular	낫다	better	낫	나
ㄷ-Irregular	듣다	listen	듣	들
ㅎ-Irregular	그렇다	to be so	그렇	그러
ㄹ-Irregular	달다	sweet	달	다
으-Irregular	쓰다	write	쓰	쓰
르-Irregular	고르다	choose	고르	골르

See Formal Polite Form of Verbs and Adjectives for examples of using original stems for conjugation. See Informal Polite Form of Verbs and Adjectives for examples of using alternate stems for conjugation.

There is no definitive rule to identify if a verb/adjective is regular or not. However, by looking at the final consonant of the original stem, you can tell it is not irregular if it does not have the irregular stem ending.

Korean verbs and adjectives are less distinguishable than those in English (e.g. walk vs beautiful), because Korean adjectives are verb-like in grammatical constructions. It does not require a verb to be (e.g. am, are, is) for an adjective to construct a sentence, and an adjective is also always the last item in a predicate or a sentence.

However, it is important to distinguish between verbs and adjectives in Korean, because even both verbs and adjectives follow a similar set of rules to derive their modified forms, the difference in the rules between verbs and adjectives are significant.

In general, you may consider a Korean verb as an action or a process, and a Korean adjective is to describe a state of being.

In English, you may simply add -ed to change a verb to its past tense. In Korean, it is done by modifying the suffix of the verb. Note that Korean adjectives are verb-like in grammatical constructions, and they conjugate just like verbs.

Past Tense of Korean Verbs and Adjectives

In order to conjugate a Korean verb or adjective to its past tense form, identify the alternate stem of its present tense form, and use 어-conjugation to attach 았다 or 었다 to it.

Exception: Use original stems to conjugate ㄹ-irregular verbs and adjectives.*

You then get the plain past tense form, which is always a regular verb.

Examples (more)

Verbs/Adjectives	Dictionary Form	Meaning	Original Stem	Alternate Stem	Plain Past Tense Form	Vowel Contraction
Regular	먹다	eat	먹	먹	먹었다	N
	하다	do	하	하	했다	Y
ㅂ-Irregular	춥다	cold	춥	추우	추웠다	Y
ㅅ-Irregular	낫다	better	낫	나	나았다	N
ㄷ-Irregular	듣다	listen	듣	들	들었다	N
ㅎ-Irregular	그렇다	to be so	그렇	그러	그랬다	Y
ㄹ-Irregular	달다	sweet	달		달았다*	N
으-Irregular	쓰다	write	쓰	쓰	썼다	Y
르-Irregular	고르다	choose	고르	골르	골랐다	Y

You can now conjugate the plain past tense form to its formal polite form, informal polite form, or informal casual form as described in the each of the rules respectively.

Present Tense	Verb / Adjective	Plain Past Tense	Formal Polite Past	Informal Polite Past	Informal Casual Past
먹다	V	먹었다	먹었습니다	먹었어요	먹었어
하다	V	했다	했습니다	했어요	했어
춥다	A	추웠다	추웠습니다	추웠어요	추웠어
낫다	A	나았다	나았습니다	나았어요	나았어
듣다	V	들었다	들었습니다	들었어요	들었어
그렇다	A	그랬다	그랬습니다	그랬어요	그랬어
달다	A	달았다	달았습니다	달았어요	달았어
쓰다	V	썼다	썼습니다	썼어요	썼어
고르다	V	골랐다	골랐습니다	골랐어요	골랐어

Compare the sentences of using the formal polite form and informal polite form of saying the same meanings in past tense:

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