Korean Vowel Dropping: Why 가 + 아요 Is 가요, Not 가아요

What you will be able to do after this lesson

• Conjugate stems that end in ㅏ or ㅓ (가, 사, 자, 만나, 서, 건너) into the polite present.
• Form their past tense: 갔어요, 샀어요, 섰어요.
• Say which vowel is dropped and why.
• Tell vowel dropping apart from the merging contractions 와요 and 마셔요.

Before you start: read vowel harmony in conjugation to know why the ending is 아요 or 어요. Time: about 25 minutes. Level: A1.

What Is Korean Vowel Dropping?

Korean vowel dropping (모음 탈락, moeum tallak) is the deletion of one vowel when two identical vowels meet at the border between a stem and an ending. Take the verb 가다 (to go). The stem is 가, which ends in ㅏ. The polite present ending is 아요, which starts with 아. Writing both gives 가아요, and Korean spelling writes only one: 가요.

The word "identical" is the key. ㅏ meets 아, and ㅓ meets 어. Because the stem vowel and the ending vowel are the same, nothing new has to be created, so one of them simply goes. Different vowels behave differently and merge, as in 오 + 아 = 와. That contrast has its own section below.

Here is the rule in two lines:

• Stem ending in ㅏ + 아 → ㅏ (가 + 아요 = 가요)
• Stem ending in ㅓ + 어 → ㅓ (서 + 어요 = 서요)

Revised Romanization (RR), the official Latin-letter system, gives gayo and seoyo as reading aids. The Hangul spelling is the form to learn. The next section shows why spelling and speech agree.

Why Is 가 + 아요 Written 가요?

가 + 아요 is written 가요 because Korean spelling shortens two identical vowels in a row to one. In speech, 가 and 아 run together without a break, so the spoken word already sounds like gayo with two syllables. The written form matches what is said. The National Institute of Korean Language (국립국어원) sets this rule in Hangul Orthography (한글 맞춤법), Article 34.

Compare 가요 and 서요: they differ only in the vowel (ㅏ against ㅓ), and the ending 요 is the same. In the full forms 가아요 and 서어요, the doubled vowel makes the syllable border audible, and standard Korean avoids it.

Worked Example: Building 만나요 and 서요 Step by Step

Take 만나다 (to meet) first.

1. Remove 다. The stem is 만나.
2. Read the last vowel. 나 has ㅏ, so the ending is 아요.
3. The stem ends in a vowel, and the ending starts with the same vowel. Drop one: 만나 + 아요 = 만나요.

Now take 서다 (to stand).

1. Remove 다. The stem is 서.
2. Read the last vowel. 서 has ㅓ, so the ending is 어요.
3. Same vowel meets same vowel. Drop one: 서 + 어요 = 서요.

Both words come out as the stem plus 요. That is the shortcut for this whole group: when the stem ends in ㅏ, ㅓ or ㅕ, write the stem and add 요.

An expert tip: dropping explains a surprise in casual speech. The casual style (해체) removes 요 from the polite form, and for these stems what remains is the bare stem. 가요 becomes 가, 사요 becomes 사, and 서요 becomes 서. A learner who sees 가 alone may think it is only a stem, but it is also a complete casual sentence meaning "I'm going" or "go?". Context and intonation tell the two apart.

The rule looks simple, so the practical question is how many stems it covers.

Which Stems Drop a Vowel?

Stems that end in ㅏ or ㅓ drop a vowel, and so do stems that end in ㅕ. The table lists 20 verbs and adjectives. Every polite present form here is a plain stem + 요 form with no extra vowel.

Two patterns help you spot the group. First, the stem's last letter is always a vowel, never a consonant, because a consonant would block the merge. Second, ㅏ-final stems are far more common than ㅓ-final stems, so 아요 is the usual ending that disappears.

ㅕ stems look different from the others, but they behave the same. 켜 + 어요 does not create a new vowel. It keeps ㅕ and loses the extra 어, so 켜요 is also dropping. Orthography Article 34 lists 켜어 → 켜 next to 가아 → 가 and 서어 → 서.

Stems that end in a consonant never drop anything: 먹 + 어요 = 먹어요 and 좋 + 아요 = 좋아요. The first step is always the same, and the 아 or 어 is chosen as explained in the present tense recipe.

The same stems matter in the past tense, where the dropped vowel returns in a new form.

Vowel Dropping in the past Tense

In the past tense, the stem vowel and 았/었 fuse into one syllable with a final ㅆ. The same dropping logic applies: 가 + 았 does not give 가았, because the duplicate ㅏ disappears and the ㅆ attaches to the stem, giving 갔. Then 어요 is added: 갔어요.

The pattern is the same for every row: present stem + ㅆ + 어요. You do not need to memorise the past forms separately. If you know 가요, you know 갔어요, and if you know 서요, you know 섰어요. The full past-tense method is in past tense conjugation.

When you say these words, the final ㅆ of the fused syllable moves forward to start the next syllable. 갔어요 is pronounced [가써요], not [갇어요]. This linking is a general rule of Korean pronunciation, explained in Korean liaison.

Dropping is one of two ways vowels combine, so the comparison below clears up a frequent mix-up.

What Is the Difference between Vowel Dropping and Contraction?

Vowel dropping removes a duplicate vowel, while contraction merges two different vowels into a new one. The deciding question is whether the stem vowel and the ending vowel are the same.

Test yourself with one question: "If I remove the ending vowel, does the stem vowel remain unchanged?" For 가요 the answer is yes. For 와요 the answer is no, because ㅗ turned into ㅘ.

Dropping is the first of seven contraction patterns taught in the polite present section. The next page, ㅘ contraction, covers the first merging case.

Vowel Dropping in Adjectives

Vowel dropping applies to adjectives whose stem ends in ㅏ or ㅓ. The adjectives 싸다, 비싸다 and 짜다 give 싸요, 비싸요 and 짜요. They follow exactly the same rule as verbs, because Korean adjectives conjugate like verbs.

Many beginner adjectives end in a consonant, so they do not drop anything: 좋다 gives 좋아요, 많다 gives 많아요, and 맛있다 gives 맛있어요. As a result, dropping looks more like a verb rule in practice, because the most frequent verbs 가다, 오다, 자다, 사다 and 타다 end in a vowel.

Vowel Dropping with Endings Other than 요

Vowel dropping happens with every ending that starts with 아 or 어, not only with 요. The ending 아서/어서 ("and then", "because"), 아도/어도 ("even if"; with 되다, "may") and 아야/어야 ("must") all lose their vowel after a ㅏ, ㅓ or ㅕ stem. Once you know the rule for 요, you know it for all of them.

Example sentences:

• 친구를 만나서 영화를 봐요. = I meet a friend and then watch a movie.
• 돈이 모자라서 못 사요. = I can't buy it because I am short of money.
• 지금 가야 해요. = I have to go now.
• 여기서 자도 돼요? = May I sleep here?

These connecting endings are taught in the grammar section. Here they show that the rule belongs to the vowels, not to the word 요.

Wrong Forms Learners Write

Learners write the full forms or stack two errors. Each wrong form below has a reason and a fix.

The last row is a past-tense error. After the ㅆ syllable, the polite ending is 어요, not 아요, even for ㅏ stems. The reason: 았/었 already did the 아/어 choice, and the ending 어요 is fixed.

If a form feels wrong, run the one-vowel test from vowel harmony in conjugation, then check whether the stem ends in a vowel.

Practice

Write the polite present and the polite past. Answers follow.

1. 사다 (buy)
2. 자다 (sleep)
3. 타다 (ride)
4. 만나다 (meet)
5. 서다 (stand)
6. 건너다 (cross)
7. 켜다 (turn on)
8. 비싸다 (be expensive)
9. Fix the error: 가아요
10. Fix the error: 서어요

Answers to the Practice

1. 사요, 샀어요 [사써요].
2. 자요, 잤어요 [자써요].
3. 타요, 탔어요 [타써요].
4. 만나요, 만났어요 [만나써요].
5. 서요, 섰어요 [서써요].
6. 건너요, 건넜어요 [건너써요].
7. 켜요, 켰어요 [켜써요].
8. 비싸요, 비쌌어요 [비싸써요].
9. 가요. The duplicate 아 drops.
10. 서요. The duplicate 어 drops.

If you missed an answer, say the polite present aloud and listen: the correct form has no pause between the stem and 요.

What to Learn Next

Korean vowel dropping is the commonest contraction in the polite present, and it is the easiest to apply: if the stem ends in ㅏ, ㅓ or ㅕ, write the stem plus 요. Next, learn how different vowels fuse in ㅘ contraction, where 오다 becomes 와요 and 보다 becomes 봐요. For the past tense in full, see past tense conjugation.

This lesson covers dropping in the polite present and past only. The ㅡ drop, the ㅐ/ㅔ stems and the merging contractions have their own pages, and the whole section is mapped on the polite present subhub. No frequency count is claimed for how many verbs follow this rule. The bracketed pronunciations are standard Seoul approximations, and the audio clips are the final reference.

Frequently Asked Questions

Why is it 가요 and not 가아요? Korean spelling shortens two identical vowels in a row to one. The stem 가 ends in ㅏ, the ending 아요 starts with 아, and the duplicate 아 is dropped. The same logic gives 서요 from 서 + 어요. Hangul Orthography (한글 맞춤법) Article 34 states the rule, so 가아요 is never written in standard Korean.

Which verbs drop a vowel? Verbs and adjectives whose stems end in ㅏ or ㅓ drop a vowel, such as 가다, 사다, 자다, 만나다, 서다 and 건너다. Stems ending in ㅕ, such as 켜다 and 펴다, also drop 어. Stems that end in a consonant, such as 먹다 or 좋다, never drop anything.

What is the past tense of 서다? The polite past of 서다 (to stand) is 섰어요 [서써요]. The stem 서 ends in ㅓ, so it takes 었, and 서 + 었 fuses into 섰 with the final ㅆ. The same pattern gives 건넜어요 from 건너다 and 켰어요 from 켜다. The formal past is 섰습니다.

Is 켜요 correct for 켜다? Yes. The polite present of 켜다 (to turn on) is 켜요. The stem 켜 ends in ㅕ, and the ending 어요 loses its 어, so 켜 + 어요 is written 켜요. The past is 켰어요. The full form 켜어요 is not used in standard writing.

Does vowel dropping happen with adjectives? Yes, when the adjective stem ends in ㅏ or ㅓ. Examples are 싸다 (cheap) giving 싸요, 비싸다 (expensive) giving 비싸요 and 짜다 (salty) giving 짜요. Many common adjectives end in a consonant, such as 좋다 and 많다, so they add 아요 in full and drop nothing.