Every Pinyin syllable with a tone needs a tone mark above one of its vowels. But which vowel gets the mark? When a syllable has two or three vowels, the answer is not always obvious. Fortunately, there is a clear, step-by-step rule that works every time.
The Rule (In Order of Priority)
Follow these steps from top to bottom. Stop as soon as you find a match:
- If the syllable contains 'a' or 'e': the tone mark goes on 'a' or 'e'. These two vowels never appear together in the same final, so there is never a conflict. Example: hǎo, méi, lái.
- If the syllable contains 'ou': the tone mark goes on the 'o'. Example: gǒu, dōu.
- Otherwise: the tone mark goes on the last vowel. This covers combinations like 'iu' and 'ui'. Example: liú, guì.
A Helpful Memory Aid
Some learners use the vowel priority phrase: a, o, e, i, u, ü. When two vowels appear together, the one that comes first in this list gets the mark. The only exception is the rule about the last vowel in 'iu' and 'ui'.
But the three-step rule above is more reliable and easier to apply without memorizing the full priority order.
Examples in Action
- shuāi: contains 'a', so the mark goes on 'a'
- duì: no 'a' or 'e', no 'ou', so the mark goes on the last vowel: 'i'
- liú: no 'a' or 'e', no 'ou', so the mark goes on the last vowel: 'u'
- guō: no 'a' or 'e', but it is not 'ou'; it is 'uo'. The 'o' here gets the mark because it is the last vowel
- lüè: contains 'e', so the mark goes on 'e'
Why 'iu' and 'ui' Are Special
Remember that 'iu' is short for 'iou' and 'ui' is short for 'uei'. In the full forms, the middle vowel ('o' or 'e') would normally take the mark. But since that middle vowel is hidden in the abbreviation, the mark shifts to the last visible vowel instead.
The Small Print: Dots and Capitals
A few typographic details trip people up. When a tone mark lands on the letter i, the i loses its own dot: you write nǐ and lì, never an i with both a dot and a mark. The letter ü is the opposite, keeping its two dots and stacking the tone mark on top, as in lǜ and nǚ. And on a capital letter the mark still goes on, so the name Ān (安) wears its tone over the capital A. The placement rule decides which vowel; these details decide how it looks.
Practice
For each syllable, decide where the tone mark belongs:
- huan: contains 'a' → mark on 'a': huán
- lei: contains 'e' → mark on 'e': léi
- diu: no 'a'/'e'/'ou' → last vowel 'u': diū
- gou: contains 'ou' → mark on 'o': gǒu
Apply the three steps in order and the answer appears every time.
