ㅣ + 어 → ㅕ and ㅚ + 어 → ㅙ (마시다 → 마셔, 되다 → 돼)

If you have ever wondered why so many Korean verbs seem to "sprout a ㅕ" in the present tense — 마시다 becoming 마셔요, 기다리다 becoming 기다려요 — the answer is a single regular rule, not a pile of exceptions. Any stem ending in ㅣ glides its ㅣ into the following -어 to make ㅕ. A parallel rule handles ㅚ-stems, and that one gives us 되다 → 돼요 — the source of the most misspelled form in the entire language. This page teaches both, and hands you a foolproof test for the 되/돼 trap.

ㅣ + 어 → ㅕ

A stem ending in ㅣ takes -어 by harmony (ㅣ is neither ㅏ nor ㅗ). The ㅣ then turns into a y-glide and fuses with 어 into one syllable, ㅕ. This is why the enormous families of verbs ending in -이다, -리다, -치다, -지다 all behave identically:

ㅚ + 어 → ㅙ, and the 되다 trap

A stem ending in ㅚ takes -어, and ㅚ + 어 fuses into ㅙ. The whole rule rides on one very common verb, 되다 ("to become / to work out / to be possible"):

• 되 + 어 → 돼 (also written out in full as 되어)

So the present of 되다 is 돼요, and this is Korean's single most infamous spelling trap. Learners — and, honestly, many native writers — reach for ×되요, because the stem looks like it should just take 요. It does not. 되 is the stem; you must add -어, and 되 + 어 fuses to 돼:

The fully written-out 되어요 is also correct and turns up in careful or formal writing, but in speech and normal writing it is 돼요.

The exact same trap has an honorific twin, 뵈다 ("to see [someone superior]," humble): 뵈 + 어 → 봬. So the polite goodbye is 봬요, and ×뵈요 is the parallel misspelling:

The 해/하 substitution test

Here is the trick that ends the 되/돼 confusion forever. 돼 behaves exactly like 해, and 되 behaves exactly like 하. So swap in a form of 하다 wherever you are unsure:

• If 해 fits, write 돼 (both are the -어 form).
• If 하 fits, write 되 (both are the bare stem).

The same test settles the past tense: since the past of 해요 is 했어요, the past of 돼요 is 됐어요 — never ×됬어요 (a spelling that mixes up the stem). If 했 works, write 됐.

The payoff carries into the past

As with every -아/어 contraction, the past is built on the same fused stem, so once you have the present you have everything:

How this differs from English

English has nothing that maps onto these glide fusions, so the temptation is to "spell it the way it's built" — writing the pieces out as ×마시어요 or ×되요 because they feel more transparent. But 마시어요 is exactly as wrong in speech as writing drinking as drink-ing: the fused form isn't a contraction of a fuller word you could fall back on, it's the word. And 되/돼 has no English analogue at all — you simply have to internalize that 돼 is 되 plus -어, the way 해 is 하 plus its ending. If you carry over just one habit from this page, make it the 해/하 test; it converts the worst spelling trap in Korean into a two-second check. The trap gets its own focused drill on the 되다 / 돼요 spelling page.

For the sister contractions on other vowel-final stems, see vowel-stem contractions, and for the harmony rule underneath all of them, vowel harmony -아/어.

Common Mistakes

1. Writing out ×마시어요 in speech. ㅣ + 어 fuses to ㅕ; the spoken and normally-written form is 마셔요.

2. The classic ×되요 for 돼요. 되 is the stem; the present needs -어, giving 돼요.

3. The ×됬어요 misspelling for the past. The past mirrors 했어요, so it is 됐어요.

4. Writing ×뵈요 for the honorific goodbye. 뵈다 patterns exactly like 되다: 뵈 + 어 → 봬.

Key Takeaways

• ㅣ + 어 → ㅕ: every -이다/-리다/-치다/-지다 stem fuses this way — 마셔요, 기다려요, 가르쳐요, 던져요. Regular, not memorized.
• ㅚ + 어 → ㅙ: 되다 → 돼요 (also spellable 되어요), 뵈다 → 봬요.
• The 되/돼 trap is settled by the 해/하 test: if 해 fits → 돼; if 하 fits → 되.
• Past tense mirrors 했어요: 돼요 → 됐어요, never ×됬어요; 마셔요 → 마셨어요.
• ×마시어요, ×되요, ×됬어요, ×뵈요 are all failures to apply the fusion — the contracted form is the only correct one.