Adverbs from Adjectives: -게, -이, -히

To say how an action is done — quietly, quickly, beautifully — you turn an adjective into a manner adverb. English has one productive suffix for this (quick → quickly) plus a handful of irregulars you just know (good → well, fast → fast). Korean works almost exactly the same way: it has one fully productive, always-safe ending — -게 — and two lexicalized endings, -이 and -히, that you memorize word by word. The single best habit you can build is knowing which situation you're in.

-게: the productive, never-fails ending

-게 attaches to any predicate stem — adjective or verb, regular or irregular — and reliably produces a manner adverb. Because Korean adjectives are descriptive verbs, -게 doesn't care about the verb/adjective divide at all; it just clamps onto the stem.

The pattern is simply stem + 게: 크다 → 크게 ("largely, loudly"), 예쁘다 → 예쁘게 ("prettily"), 조용하다 → 조용하게 ("quietly"), 행복하다 → 행복하게 ("happily"), 맛있다 → 맛있게 ("deliciously"). No irregular stems block it, no exceptions apply. If you remember one thing from this page: when you're unsure how to make an adverb, use -게 — it is always acceptable.

-이: a lexicalized set, not a rule

-이 produces a small, fixed group of very common adverbs. Do not try to derive these — learn them as vocabulary. The most frequent ones:

• 많이 ("a lot, much") — from 많다
• 같이 ("together") — from 같다
• 깨끗이 ("cleanly, thoroughly") — from 깨끗하다
• 없이 ("without") — from 없다

Note the pronunciations that the spelling hides: 많이 is [마니] (mani, the ㅎ drops), and 같이 is [가치] (gachi, the ㅌ palatalizes to ㅊ before -이). These are exactly the kinds of sound changes that make -이 words feel unpredictable — another reason to file them under vocabulary.

-히: also lexicalized, mostly from 하다-adjectives

-히 attaches largely to adjectives whose dictionary form ends in 하다, and again the set is memorized rather than derived:

• 조용히 ("quietly") — from 조용하다
• 열심히 ("diligently, hard") — a fixed adverb; note there is no free-standing adjective ×열심하다 in everyday use
• 급히 ("hastily, urgently") — from 급하다
• 안녕히 ("in peace") — the 안녕히 계세요 / 안녕히 가세요 of every goodbye

Honest difficulty: -이 vs -히 is not predictable

There is no reliable rule that tells you whether a 하다-adjective takes -이 or -히. 깨끗하다 gives 깨끗이 (with -이), but 조용하다 gives 조용히 (with -히), and 급하다 gives 급히. The official spelling convention keys off whether the adverb is pronounced [이], [히], or either — which is circular for a learner, since you'd have to already know the pronunciation. The practical consequence: treat -이 and -히 words as spellings to memorize, and lean on -게 whenever you're building an adverb fresh. 조용하게 is always available and always correct, even though native speakers happen to say 조용히.

Two suppletive adverbs worth flagging: 잘, 빨리

A couple of the most common adverbs don't come from any adjective at all — like English well (there's no adjective goodly):

• 잘 ("well") — 잘 자요 ("sleep well"), 잘 먹었어요 ("that was a good meal"). There's no adjective 잘다 meaning "good"; 잘 simply *is the adverb.
• 빨리 ("quickly") — the everyday adverb from 빠르다 ("to be fast"), but frozen in this shape.

Common Mistakes

1. Inventing an -이 form by analogy. 조용하다 does not give ×조용이; the fixed adverb is 조용히 (and 조용하게 is always safe).

2. Attaching -게 or -이 to a word that takes -히. 열심히 is the fixed adverb; ×열심게 and ×열심이 are both wrong.

3. Spelling 깨끗이 as ×깨끗히. This one is a genuine spelling trap even for natives — the standard spelling is 깨끗이, with -이.

4. Confusing 같이 (adverb) with 같다 (adjective). 같이 means "together" (an adverb); 같다 means "to be the same" (an adjective). They look related but do different jobs.

Key Takeaways

• -게 is the fully productive, always-correct manner-adverb ending — it attaches to any adjective or verb stem (크게, 조용하게, 맛있게). When in doubt, use -게.
• -이 (많이, 같이, 깨끗이, 없이) and -히 (조용히, 열심히, 급히, 안녕히) are lexicalized — memorize them as vocabulary; they aren't derived by rule.
• -이 vs -히 is not predictable — 깨끗이 but 조용히 — so learn the spelling and fall back on -게 for anything new.
• A few key adverbs are suppletive: 잘 ("well"), 빨리 ("quickly"), with no adjective to derive them from.
• Watch the sound changes hidden in spelling: 많이 → [마니], 같이 → [가치].