Tone Mark Placement Rules
Where exactly do tone marks go? Master the orthographic rules.
The Challenge
Vietnamese has 6 tones (including the level tone with no mark). When a syllable has multiple vowels, which vowel gets the tone mark?
This lesson provides the complete algorithmic rules for tone mark placement. These rules are essential for correct spelling and reading.
⚠️ Key Principle:
The tone mark goes on the main vowel (nucleus) of the syllable, but the exact position depends on the vowel combination. There are systematic rules—not random placement!
1. The 6 Tones (Quick Review)
Level / Mid tone
No diacritic mark
Rising / Sharp tone
Acute accent ( ́ )
Falling / Heavy tone
Grave accent ( ̀ )
Dipping-rising / Question tone
Hook above ( ̉ )
Glottalized rising / Tumbling tone
Tilde ( ̃ )
Glottalized falling / Heavy drop tone
Dot below ( ̣ )
2. Simple Case: Single Vowel Syllables
When there's only one vowel in the syllable, the tone mark always goes on that vowel. Easy!
ba(three)
Single vowel: a
bá(uncle)
Mark on: á
mẹ(mother)
Single vowel: e
tô(bowl)
Mark on: ô
tư(private)
Single vowel: ư
tỉ(billion)
Mark on: ỉ
băn(worry)
Single vowel: ă
bẵng(long time)
Mark on: ẵ
✓ Rule 1 (Single Vowel):
If the syllable has only one vowel letter, the tone mark goes on that vowel.
3. Complex Case: Multiple Vowels (Diphthongs & Triphthongs)
When there are 2 or 3 vowels together, which one gets the tone mark? Vietnamese follows a priority system.
The Placement Algorithm
Follow these rules in order. Stop when you find a match:
- If there's a "ô", "ơ", "ê", "ă", "â", or "ư": The tone mark goes on that special vowel (they're always the nucleus).
- If there are 3 vowels: The tone mark goes on the second vowel (middle vowel).
- If there are 2 vowels and the second is "i" or "u": The tone mark goes on the first vowel (the "i" or "u" is a glide/semivowel).
- If there are 2 vowels and neither is "i" or "u" at the end: The tone mark goes on the second vowel (it's the nucleus).
Rule 2Special Vowels Always Get the Mark
The vowels ô, ơ, ê, ă, â, ư are always the nucleus when they appear. If you see one of these, put the tone mark on it—no exceptions!
| Special Vowel | Example Word | English | Why |
|---|---|---|---|
| ô | môi(lips) | lips | ô is the nucleus (not o + i) |
| ơ | cơm(rice) | rice | ơ is always nucleus |
| ê | tên(name) | name | ê is always nucleus |
| ă | năm(five) | five | ă is always nucleus |
| â | cây(tree) | tree | â is the nucleus (not a + y) |
| ư | tưới(water (plants)) | water (plants) | ư is the nucleus |
✓ Correct:
hỏi(ask) — mark on "ỏ" (ô is nucleus)
mới(new) — mark on "ớ" (ơ is nucleus)
quên(forget) — mark on "ê" (ê is nucleus)
✗ Wrong:
hỏi — *hởi (can't put mark on i)
mới — *mơí (can't skip ơ)
quên — *quèn (can't skip ê)
Rule 3Three Vowels: Mark the Middle Vowel
Triphthongs (3-vowel combinations) like oai, uôi, ươi, uya get the tone mark on the second (middle) vowel.
| Triphthong | Structure | Mark Goes On | Example |
|---|---|---|---|
| oai | o + a + i | a (middle) | ngoài(outside) |
| uôi | u + ô + i | ô (middle, also special) | cười(laugh) |
| ươi | ư + ơ + i | ơ (middle, also special) | người(person) |
| uya | u + y + a | y (middle) | huyền(dark; mysterious) |
| oay | o + a + y | a (middle) | khoảng(about) (in khoay(stir)) |
✓ Correct:
ngoài(outside) — 3 vowels: o-a-i, mark on "à"
người(person) — 3 vowels: ư-ơ-i, mark on "ơ"
tuyển(select) — 3 vowels: u-y-ê, mark on "y"
✗ Wrong:
*ngoải — can't put mark on first vowel
*ngườì — can't put mark on final i
*tủyên — can't put mark on first vowel
Rule 4Two Vowels Ending in -i or -u: Mark the First
When you have 2 vowels and the second one is "i" or "u", the tone mark goes on the first vowel. The final "i" or "u" acts as a glide/off-glide, not the nucleus.
| Diphthong | Structure | Mark Goes On | Example |
|---|---|---|---|
| ai | a + i | a (first) | mai(tomorrow) |
| ao | a + o (= /aw/) | a (first) | sào(pole) |
| au | a + u | a (first) | dấu(sign) |
| âu | â + u | â (first, also special) | lâu(long time) |
| ây | â + y | â (first, also special) | mây(cloud) |
| oi | o + i | o (first) | tôi(I) (ô + i → ô) |
| ơi | ơ + i | ơ (first, also special) | cơi(winnow) |
| ui | u + i | u (first) | tùi(bag) |
| ưu | ư + u | ư (first, also special) | ưu(excellent) |
| ay | a + y | a (first) | tay(hand) |
✓ Correct:
mái(roof) — ai → mark on "á"
đầu(head) — âu → mark on "ầ"
hỏi(ask) — ôi → mark on "ỏ"
tay(hand) — ay → (no mark, level tone)
✗ Wrong:
*maí — can't put mark on i
*đâú — can't put mark on u
*hôí — can't skip ô and put on i
*taý — can't put mark on y
Rule 5Two Vowels (Other Cases): Mark the Second
When you have 2 vowels and the second one is NOT "i" or "u", the tone mark typically goes on the second vowel (it's the nucleus). This is less common.
| Combination | Structure | Mark Goes On | Example |
|---|---|---|---|
| oa | o + a | a (second) | hòa(peace) |
| oe | o + e | e (second) | khoẻ(healthy) (rare) |
| ua | u + a | a (second) | mùa(season) |
| ưa | ư + a | a (second) — but ư is special! | mưa(rain) |
| ia | i + a | a (second) | kia(over there) |
⚠️ Special Note:
For ưa, even though Rule 2 says "special vowels get the mark", the tone actually goes on "a" because "ưa" is analyzed as /ɯə/ where "a" is the main vowel. Similarly for ươ (ư + ơ), the mark goes on "ơ".
✓ Correct:
hòa(peace) — oa → mark on "à"
mùa(season) — ua → mark on "à"
mưa(rain) — ưa → mark on "a" (not ư!)
✗ Wrong:
*hỏa — can't put mark on first vowel
*mủa — can't put mark on first vowel
*mứa — can't put mark on ư (exception!)
4. Complete Tone Placement Algorithm
Decision Tree for Tone Mark Placement
START: Count the vowel letters in the syllable
✓ Only 1 vowel?
→ Put tone mark on that vowel.
Example: tô, mẹ, bắn
✓ Contains ô, ơ, ê, ă, â, or ư?
→ Put tone mark on that special vowel (with exceptions for ưa, ươ).
Example: môi (on ô), quên (on ê), cây (on â)
⚠️ Exception: mưa → mark on "a", lươn → mark on "ơ"
✓ Has 3 vowels (triphthong)?
→ Put tone mark on the middle (2nd) vowel.
Example: ngoài (o-a-i → mark on "a"), người (ư-ơ-i → mark on "ơ")
✓ Has 2 vowels ending in -i or -u?
→ Put tone mark on the first vowel.
Example: mái (ai → mark on "a"), đầu (âu → mark on "â"), hỏi (ôi → mark on "ô")
✓ Has 2 vowels NOT ending in -i/-u?
→ Put tone mark on the second vowel.
Example: hòa (oa → mark on "a"), mùa (ua → mark on "a")
END: Tone mark placed!
5. Common Mistakes & Edge Cases
❌ Mistake 1: Putting mark on final -i or -u in diphthongs
✗ Wrong:
*maí (should be mái)
*thoí (should be thói)
*đaú (should be đáu)
✓ Correct:
mái(roof) — mark on "á", not "i"
thói(habit) — mark on "ó", not "i"
đáu(where (South)) — mark on "á", not "u"
Why: In diphthongs ending in -i or -u, the final letter is a glide (off-glide), not the nucleus. The tone mark goes on the main vowel.
❌ Mistake 2: Skipping special vowels (ô, ơ, ê, ă, â, ư)
✗ Wrong:
*mởi (should be mới)
*quèn (should be quên)
*cáy (should be cây)
✓ Correct:
mới(new) — mark on "ớ" (ơ is special)
quên(forget) — mark on "ê" (ê is special)
cây(tree) — mark on "â" (â is special)
Why: Special vowels (with diacritics) are ALWAYS the nucleus. You can't skip them.
❌ Mistake 3: Wrong vowel in triphthongs
✗ Wrong:
*ngoải (should be ngoài)
*ngươì (should be người)
✓ Correct:
ngoài(outside) — 3 vowels: mark on middle "à"
người(person) — 3 vowels: mark on middle "ơ"
Why: Triphthongs always have the tone mark on the second (middle) vowel.
⚠️ Edge Case: ưa and ươ exceptions
Even though ư and ơ are "special vowels," in the combinations ưa and ươ, the tone mark goes on the SECOND vowel (a or ơ), not on ư.
✓ Correct:
mưa(rain) — mark on "a" (not ư!)
lươn(eel) — mark on "ơ" (not ư!)
thừa(excess) — mark on "a"
chương(chapter) — mark on "ơ"
✗ Wrong:
*mứa — can't put on ư
*lứơn — can't put on ư
*thứa — can't put on ư
*chứơng — can't put on ư
💡 Why this exception?
Phonetically, "ưa" = /ɯə/ and "ươ" = /ɯə/, where "ư" acts as a medial glide before the nucleus "a" or "ơ". So the tone mark follows the nucleus, not the glide.
6. Practice: Apply the Rules
For each word, identify where the tone mark should go and why.
Exercise 1: Single vowel or complex?
Identify the vowel combination and apply the correct rule.
hoa(flower)
Vowels: o + a (2 vowels)
Rule: 2 vowels, second is NOT i/u → mark on 2nd vowel
Mark on: "a"
✓ With sắc tone: hoá(change)
khai(open)
Vowels: a + i (2 vowels)
Rule: 2 vowels ending in -i → mark on 1st vowel
Mark on: "a"
✓ With huyền tone: khài(to cough (alt.))
thuoc(medicine)
Vowels: u + o (2 vowels)
Rule: 2 vowels, but "o" at end (acts like /w/) → mark on "u"
Mark on: "u"
✓ With hỏi tone: thuỏc (rare)
chuoi(banana)
Vowels: u + o + i (3 vowels)
Rule: 3 vowels → mark on middle (2nd) vowel
Mark on: "o"
✓ With acute tone: chuối(banana)
Exercise 2: Special vowels
Find the special vowel and apply Rule 2.
doi(demand)
Special vowel: ô
Rule: ô is always nucleus → mark on ô
Mark on: "ô"
✓ With hỏi tone: đổi(change)
nhuom(dye)
Special vowel: ươ (ư + ơ)
Rule: ươ combination → mark on "ơ" (exception!)
Mark on: "ơ"
✓ With ngã tone: nhuộm(dye)
7. Quick Reference: Tone Placement Patterns
| Pattern | Rule | Mark Position | Examples |
|---|---|---|---|
| Single vowel | Only 1 vowel | On that vowel | mẹ, tô, bắn |
| ô, ơ, ê, ă, â, ư | Special vowel present | On special vowel | môi, tên, cây |
| oai, uôi, ươi | 3 vowels (triphthong) | On 2nd (middle) | ngoài, cười, người |
| ai, ao, au, ây, ôi, ưu | 2 vowels ending -i/-u | On 1st vowel | mái, đầu, hỏi |
| oa, ua, ia | 2 vowels NOT ending -i/-u | On 2nd vowel | hòa, mùa, kìa |
| ưa, ươ | Exception: ư + vowel | On 2nd (a or ơ) | mưa, lươn, thừa |
Summary: Master These 5 Rules
- Single vowel: Mark goes on that vowel
- Special vowels (ô, ơ, ê, ă, â, ư): Mark goes on special vowel (except ưa, ươ)
- Three vowels: Mark goes on middle vowel
- Two vowels ending -i/-u: Mark goes on first vowel
- Two vowels (other): Mark goes on second vowel
Practice these rules until they become automatic. Correct tone placement is essential for proper Vietnamese spelling!