是 (shì) is the Chinese "to be," but it is far narrower than English be. Its single, native job is to equate two nouns — to say that X is Y, that one thing belongs to a category or is identical to another. English be also does the work of describing ("she is tall") and locating ("the book is on the table"); Chinese hands those two jobs to completely different words — a bare adjective with 很, and the verb 在. So the reframing that saves you months of errors is: 是 only for noun = noun. The moment the thing after "is" is an adjective or a place, 是 is the wrong word.
Sense 1: X = Y (identity and category)
This is the core. 是 sits between two noun phrases and says they are the same thing, or that the first falls into the second's category — name, nationality, job, relationship, day of the week. Negate it with 不是 (bú shì), never with 没.
你好，我是李明，是这里的新同事。
nǐ hǎo, wǒ shì Lǐ Míng, shì zhèlǐ de xīn tóngshì
Hi, I'm Li Ming — I'm the new colleague here.
这不是我的手机，是我姐姐的。
zhè bú shì wǒ de shǒujī, shì wǒ jiějie de
This isn't my phone, it's my sister's.
你是哪国人？——我是加拿大人。
nǐ shì nǎ guó rén? —— wǒ shì Jiānádà rén
What nationality are you? — I'm Canadian.
今天不是星期一，是星期二。
jīntiān bú shì xīngqīyī, shì xīngqī'èr
Today isn't Monday, it's Tuesday.
Sense 2: the 是…的 emphasis frame
是 also opens the 是…的 frame, which fences off a known action and spotlights one detail of it — when, where, how, or by whom it happened. In 我是昨天来的, the arrival is taken for granted; 是…的 puts the focus on 昨天. This is its own construction with its own rules, so it is taught in full on the 是…的 construction page — here just recognise that this 是 is not the plain copula.
我是坐地铁来的，不是开车。
wǒ shì zuò dìtiě lái de, bú shì kāichē
I came by subway, not by car.
这件事是他先告诉我的。
zhè jiàn shì shì tā xiān gàosu wǒ de
It was he who told me about this first.
Sense 3: stressed 是 for emphatic affirmation
Say 是 with heavy stress and it stops being the copula and becomes an emphasis marker meaning "it really is true that / indeed." This stressed 是 is the one place you will legitimately see 是 in front of a verb or even an adjective — because here it is not linking noun to noun, it is asserting the truth of the whole clause. It usually sets up a "yes, but" concession, often with a following 就是 / 可是.
我是不知道，你别再问我了。
wǒ shì bù zhīdào, nǐ bié zài wèn wǒ le
I honestly don't know — stop asking me. (informal)
这个菜是好吃，就是有点儿贵。
zhège cài shì hǎochī, jiùshì yǒudiǎnr guì
This dish IS tasty — it's just a little pricey. (informal, concessive)
Sense 4: 是 for "what fills a place" (existential)
When a location word comes first, 是 can describe what a place is entirely occupied by — 门口是一家便利店 "at the entrance there's a convenience store." Careful: this overlaps with 有 but is not the same. 桌上有书 means "there are books (among other things)"; 桌上是书 means "what's on the table is books" — books fill it, take it over. 有 lists existence; 是 identifies the whole content.
出了车站，对面就是我们的酒店。
chū le chēzhàn, duìmiàn jiùshì wǒmen de jiǔdiàn
Coming out of the station, the building right across is our hotel.
他桌子上全是书，连放杯子的地方都没有。
tā zhuōzi shàng quán shì shū, lián fàng bēizi de dìfang dōu méiyǒu
His desk is all books — there's not even room for a cup.
Key patterns built on 是
| Phrase | Pinyin | Meaning |
|---|---|---|
| 是的 / 是 | shì de / shì | yes (answering a 是 question) |
| 是不是 | shì bu shì | is it…? (A-not-A question) |
| 就是 | jiùshì | exactly / precisely / it's just that |
| 还是 | háishi | or (in questions) / still |
| 要是 | yàoshi | if (informal) |
| 但是 / 可是 | dànshì / kěshì | but |
| 于是 | yúshì | thereupon, and so |
| 不是…而是… | bú shì… érshì… | not X but Y |
| 是…的话 | shì… de huà | if it is the case that… |
Grammar notes
Negation is always 不是; 是 belongs to the small set of verbs (with 在, 姓, 像) that reject 没. To ask a yes/no question, either add 吗 (你是学生吗？) or use the A-not-A form 是不是 (你是不是学生？). A whole family of connectors — 但是, 可是, 于是, 要是, 还是 — are frozen compounds of 是; you learn them as words, not as live copulas.
The deepest source of error is the three-way split English be forces into Chinese. Keep them apart: 是 for noun = noun, bare adjective + 很 for descriptions (see stative verbs take no 是 and adjectives are stative verbs), and 在 for location. The overlap between 是, 有 and 在 in existential sentences is mapped on the 是 / 有 / 在 contrast page.
Common Mistakes
1. Putting 是 before an adjective. Descriptions use a bare adjective with 很, not 是. (The only exception is the stressed emphatic 是 of Sense 3.)
❌ 我今天是很累。
Incorrect — 累 is an adjective; 'I'm tired' is 我今天很累, no 是.
✅ 我今天很累。
wǒ jīntiān hěn lèi
I'm really tired today.
2. Using 是 for plain location. "X is at/on a place" is 在, not 是.
❌ 我的钥匙是桌子上。
Incorrect — location takes 在: 我的钥匙在桌子上.
✅ 我的钥匙在桌子上。
wǒ de yàoshi zài zhuōzi shàng
My keys are on the table.
3. Negating 是 with 没. 是 is one of the verbs that only ever take 不.
❌ 他没是我们的老师。
Incorrect — 是 negates with 不, never 没: 他不是我们的老师.
✅ 他不是我们的老师。
tā bú shì wǒmen de lǎoshī
He isn't our teacher.
4. Answering every yes/no question with 是的. Only 是-questions get 是 back; other verbs echo the verb itself.
❌ 你去吗？——是的。
Incorrect — a 去 question is answered by echoing the verb: 去 / 我去.
✅ 你去吗？——去。
nǐ qù ma? —— qù
Are you going? — Yeah (I'm going).
Key Takeaways
- 是 does one job: it equates two nouns (X = Y — identity, category, name, day).
- It does not go before adjectives (她很高, not 她是高) and does *not mark location (书在桌子上, not *书是桌子上).
- Negate only with 不是; question with 吗 or the A-not-A 是不是.
- Stressed 是 (Sense 3) is an emphasis marker, not the copula — that's the one time it precedes a verb/adjective.
- Existential 是 (门口是…) says a place is filled by something; 有 only lists that something exists there.
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- 在 (zài) — be at / progressive / -ingHSK 1 — 在 (zài) is the verb 'be located at' (我在家), the location coverb that sits BEFORE the verb (在家吃饭), and the progressive marker 'be V-ing' (他在打电话) — three linked uses of one word.
- 有 (yǒu) — have / there is / existHSK 1 — 有 (yǒu) covers both 'have/possess' (我有一个哥哥) and 'there is/exists' (桌子上有一本书); it is the ONE verb negated with 没, never 不 — the negative is always 没有, never *不有.
- The Copula 是 (shì): A is BHSK 1 — 是 (shì) links two nouns — 我是学生, 这是我的书. It is ONLY for noun = noun. It is NOT used before adjectives (你很高, never 你是高), NOT for location (在, not 是), and NOT for possession (有). English 'be' fans out into several Chinese patterns; 是 is just one of them.