Which Verbs Take Which Suffix (and Why It Is Unpredictable)

If you have read the seven suffix pages (이/히/리/기/우/구/추), you may be hoping this page hands you the master rule — feed a verb in, get the right suffix out. It cannot, because no such rule exists. The morphological causative is not productive: only a closed, historically inherited set of verbs has a fused causative at all, and which suffix each one takes is settled by tradition, not by any law you can apply live. This is the reality-check page. Its job is to give you the genuine tendencies (they exist, and they help), to be blunt about where they break, and to hand you the one thing that is always safe — the productive fallback V-게 하다.

The tendencies (real, but only tendencies)

The stem-final consonant biases the choice of suffix. If you already know a verb has a fused causative and you are trying to recall its shape, these are the odds to bet on:

These are worth internalizing as recall aids. But look again at the ㄱ row: 먹다 takes 이 (먹이다) while 익다, also ㄱ-final, takes 히 (익히다), and 속다 takes 이 again (속이다). Same final consonant, different suffixes. The phonology narrows the field; it does not decide the winner.

Where the tendencies simply fail

Two things break any attempt to treat the table as a rule.

First, a fused form can carry a meaning you would never predict. The suffix is there, but the verb has drifted into something non-compositional, so even "correctly" guessing the shape can land you on the wrong meaning:

• 놀다 ("play") → 놀리다 does not mean "make play." It means tease / make fun of (사람을 놀리다) or leave idle (돈을 놀리다).
• 웃다 ("laugh") → 웃기다 is "make laugh," but has also become the slang adjective "hilarious / ridiculous."
• 살다 ("live") → 살리다 is "save a life," and 죽다 ("die") → 죽이다 is "kill" — both fully lexicalized, not transparent "cause to live/die."

Second, and more important: most verbs have no fused causative at all. There is simply no morphological causative for 가다, 오다, 마시다, 만나다, 배우다, 쉬다, 걷다, 뛰다, or any Sino-Korean 하다-verb. For these there is nothing to remember and nothing to invent — you must use a periphrastic strategy.

The decision procedure that actually works

Instead of a suffix rule, use a three-step routine. It never fails, because the last step always applies.

Step 1 — Do you already know a fused causative for this verb? If it is on your memorized list (먹이다, 입히다, 울리다, 웃기다, 재우다, 낮추다…), use it. Where a fused form exists, it is usually the more idiomatic, hands-on choice.

Step 2 — Is the verb a Sino-Korean noun + 하다? Then swap 하다 for 시키다: 공부하다 → 공부시키다, 정지하다 → 정지시키다. See N시키다.

Step 3 — Otherwise (or whenever you are unsure): use V-게 하다. It attaches to any verb, needs no memorization, and is always grammatical. This is your default.

Why English speakers over-reach here

English has exactly one causative habit — the analytic "make/let/have/get + verb" — and it works on everything, so English speakers are used to a fully productive system. Korean's fused causatives look like a similar productive machine (add a little suffix, get a causative), and the temptation is to run that machine on every verb. But the fused system is the opposite of productive: it is a museum of inherited forms. The correct mental model is that Korean's productive causative is 게 하다 (that is the true parallel to English "make eat"), and the suffixes are a bonus vocabulary layer sitting on top of a closed list of verbs.

A note on the passive overlap

One more reason not to derive freely: the suffixes 이/히/리/기 also build passives, and for some stems the same shape you might guess for a causative is actually the established passive. 먹다 has 먹히다 — but that is the passive "be eaten," not a causative "feed" (feed is 먹이다, with 이). 잡다 → 잡히다 is "be caught," a passive, not "make catch." So a wrong guess doesn't just fail; it can produce a real word with the opposite valency. The overlap set is collected on the passive/causative homophone page.

Common Mistakes

1. Inventing a fused causative for a verb that has none. 가다, 오다 and their kind take 게 하다.

2. Pattern-matching the ㄱ row onto 익다. Final ㄱ does not force 이; 익다 takes 히.

3. Assuming a fused form means the plain causative. 놀리다 is "tease," not "make play."

4. Putting a suffix on a Sino-하다 verb. Use 시키다 (or 게 하다), never a fused suffix.

Key Takeaways

• The fused causative is a closed, memorized set — the stem-final consonant only hints at the suffix and often guesses wrong (먹이다 vs 익히다).
• Many verbs (가다, 오다, 마시다, all 하다-verbs) have no fused causative — there is nothing to invent.
• Some fused forms are lexicalized (놀리다 = tease, 죽이다 = kill), so even the right shape can be the wrong meaning.
• The suffixes 이/히/리/기 double as passives (먹히다, 잡히다) — a bad guess can flip the valency.
• The reliable routine: known fused form → use it; Sino-하다 → 시키다; otherwise → V-게 하다, which never fails.