Most learners meet pinyin as "the pronunciation letters under the characters" and absorb its spelling by repetition. That works until you have to write pinyin — on a flashcard, in a text message, or for a teacher — and suddenly the questions appear: does keep its dots? Why is spelled with a w when the final is just u? Which vowel carries the tone mark in ? The answers are a small set of rules, all older than the textbooks that quietly apply them, and all worth learning once.
Initials and finals at a glance
A Mandarin syllable in pinyin has at most three parts: an initial (the consonant that starts it), a final (the vowel part, sometimes with a consonant ending like n or ng), and a tone mark. There are 21 initials — b, p, m, f, d, t, n, l, g, k, h, j, q, x, zh, ch, sh, r, z, c, s — and about 35 finals, from simple ones like a, o, e to compound ones like , , and . A syllable can also skip the initial entirely, which is where y and w come in below.
Two sounds deserve a warning for English ears, because the letters mislead. The pinyin letter is a "ts" sound, as in the "ts" of "cats" — so 菜 (, vegetable) sounds like "tsai". And is a "ch"-like sound made with the tongue flat, so 七 (, seven) is closer to "chi" than "ki". Similarly is a retroflex "j" and is a soft "sh". If you remember nothing else: pinyin q, x, c, and zh are not their English letter sounds, and every other letter is roughly familiar.
The ü rule: when the dots disappear
The sound — say "ee" while rounding your lips as for "oo" — is written with two dots only in a minority of syllables. The rule: after j, q, x, and y, the ü loses its dots and is written as plain u, because after those four initials the plain u sound does not exist in Mandarin, so no confusion is possible:
去 — to go (written qu, pronounced qü)
需要 — to need (xu = xü)
句子 — sentence (ju = jü)
鱼 — fish (yu = ü)
After the initials l and n, by contrast, both u and ü exist as separate sounds, so the dots stay to keep the pairs apart:
旅 — travel, versus 鲁 — a surname
女 — woman, versus 努 — to strive
Practical consequence: when you type pinyin into an input method, the ü key does not exist, so you type instead — produces . And when a converter gives you with a plain u, trust it: the u after q is always ü under the hood. ToPinyin's converter follows the standard convention and keeps ü written out after l and n, so your annotations always match textbook spelling.
y and w as separators
When a syllable begins with the vowels i, u, or ü and has no initial consonant, pinyin does not just write the bare vowel — the letter changes to y or w (or their combination) to mark the syllable boundary clearly:
- i at the start becomes y: 一 is , not "i"; 眼 is ; 音 is .
- u at the start becomes w: 五 is , not "u"; 我 is .
- ü at the start becomes yu: 鱼 is ; 月 is .
- In compound finals, only the first letter changes: → (as in 鸭), → ( 要), → ( 外), and is written ( 喂).
Why bother? Because Chinese text written in pinyin has no spaces between syllables inside a word, and a bare vowel at a word edge would run into the neighbors. The y and w act as built-in walls. You will also meet one special case: the syllable never stands alone — it always appears attached to an initial like d or zh; and the syllables and never appear bare either, because they have already become and .
Where the tone mark goes
A tone mark sits on exactly one vowel of the syllable, chosen by a fixed order of precedence: a beats o and e, which beat i, u, and ü. If the syllable contains an a, the mark goes on the a (, ). If there is no a but there is an o or e, it goes there (, ). The main exception: in the pairs iu and ui, the mark goes on the second letter — (six), (correct), is a different case where o follows u but o wins by rule two. And the ü dot rule interacts with tones in one pretty way: when a tone mark lands on ü, the two pronunciation dots come off but the tone mark stays — 绿 is written , one mark, not three dots stacked.
好 — the a carries the mark
六 — iu marks the u
对 — ui marks the i
When tones are written as numbers instead (, ), the placement question disappears — that is one reason dictionaries and flashcard apps often use numbers. The converter on this site outputs both styles, so you can read tone marks on screen and copy tone numbers into an app. Which style to choose when is mostly a question of where the text is going; the tones guide covers what the marks themselves mean.
Apostrophes that prevent misreading
The last rule is tiny but saves real confusion. When a syllable starting with a, o, or e follows another syllable inside the same word, pinyin inserts an apostrophe before it — otherwise the two would blur into one apparent syllable. The textbook example is the city of Xi'an:
西安 — the city (two syllables: xī + ān)
先 — first (one syllable)
Without the apostrophe, "Xīān" would be unreadable: is it xi-ān or a weird xian? The apostrophe answers. You will meet it again in 天安门 (Tiananmen) and in names like (Chang'e, the moon goddess). Note the asymmetry: an apostrophe is only used before a, o, and e — syllables starting with i, u, or ü never need one, because y and w already mark the boundary, as above. That is the whole system working together: y and w wall off the one side, the apostrophe walls off the other.
With these five rules — the inventory, the ü dots, y and w, tone-mark placement, and the apostrophe — you can write any Mandarin syllable correctly from memory. The fastest way to make it stick is productive use: write a sentence's pinyin yourself, then check it against the machine's answer.