知道 (zhīdào) means "to know" in the sense of holding a fact or piece of information — knowing that something is the case, knowing who / where / when. English "know" is a single overworked word that Chinese splits across four verbs, and 知道 is only one of them: it is not for knowing a person (认识 rènshi), not for knowing how to do something (会 huì), and not for understanding (懂 dǒng / 明白 míngbai). Getting these apart is one of the highest-value distinctions for beginners — see 知道 vs 认识.
Sense 1: know a fact / know that…
知道 happily takes a whole clause as its object — 我知道 + [他今天不来]. This is where it differs most from English, which needs "know that"; Chinese just juxtaposes the clause.
我知道他今天不来。
wǒ zhīdào tā jīntiān bù lái
I know (that) he's not coming today. — a full clause as the object.
这件事全公司都知道了。
zhè jiàn shì quán gōngsī dōu zhīdào le
The whole company knows about this now. — 了 marks the new state of knowing.
我早就知道你会来。
wǒ zǎo jiù zhīdào nǐ huì lái
I knew all along you'd come.
Sense 2: know who / where / whether (embedded questions)
知道 also takes an embedded question — 谁, 哪儿, 什么, or a 是不是 clause. The key rule for English speakers: an embedded question inside 知道 takes no 吗. The 吗 only appears once, at the very end, if the whole sentence is a yes/no question. See embedded questions.
你知道洗手间在哪儿吗？
nǐ zhīdào xǐshǒujiān zài nǎr ma
Do you know where the restroom is? — 吗 belongs to the whole question, not to 在哪儿.
我不知道该说什么。
wǒ bù zhīdào gāi shuō shénme
I don't know what to say. — embedded 'what', no 吗.
你知道他是不是中国人吗？
nǐ zhīdào tā shì bú shì Zhōngguó rén ma
Do you know whether he's Chinese? — embedded A-not-A + final 吗.
Sense 3: 我知道了 — got it, I see
The stock reply 我知道了 (wǒ zhīdào le) means "got it / understood / I see." The 了 marks the change into a knowing state — you didn't know, now you do. Bare 我知道 (no 了) sounds like "I (already) know," which can come across as curt or impatient.
好的，我知道了，谢谢提醒。
hǎo de, wǒ zhīdào le, xièxie tíxǐng
Okay, got it — thanks for the reminder.
——记得带伞。——知道了，妈！
—— jìde dài sǎn. —— zhīdào le, mā!
'Remember to take an umbrella.' 'I know, Mom!' — mildly exasperated 知道了.
Sense 4: 不知道 / 谁知道呢
The negative 不知道 "don't know" is one of the most-used phrases in the language, and the rhetorical 谁知道呢 "who knows?" expresses a shrug.
我也不知道，你去问问他吧。
wǒ yě bù zhīdào, nǐ qù wènwen tā ba
I don't know either — go ask him.
谁知道呢，也许明天就好了。
shéi zhīdào ne, yěxǔ míngtiān jiù hǎo le
Who knows — maybe it'll be fine by tomorrow.
Know, but not know: 知道 vs 认识
| Verb | Pinyin | "Know" as… |
|---|---|---|
| 知道 | zhīdào | know a fact / that… (I know who he is) |
| 认识 | rènshi | be acquainted with a person/place (I know him) |
| 会 | huì | know how to (I know how to swim) |
| 懂 / 明白 | dǒng / míngbai | understand, grasp (I understand) |
我知道这个人，但是不认识他。
wǒ zhīdào zhège rén, dànshì bú rènshi tā
I know of this person, but I don't know him personally. — 知道 (of) vs 认识 (acquainted).
Grammar notes
知道 is a two-syllable verb, so it does not reduplicate the way monosyllabic verbs do (no 知知道) — to soften it you lean on 了 or context, not reduplication. It resists the progressive 在 and durative 着 because knowing is a *state, not an action in progress: "I'm knowing" is ungrammatical in Chinese too. Note the tone/neutral-tone variation: the second syllable is often light (zhīdao) in fast speech, though the citation form is zhīdào. For the fine line between "know the information" (知道) and "grasp / understand" (懂), see 懂 (dǒng).
Common Mistakes
1. Using 知道 to mean 'know a person'. 知道他 is "know of him / know a fact about him"; being acquainted is 认识.
❌ 我知道你姐姐，我们是同学。
Wrong — being acquainted with a person is 认识, not 知道.
✅ 我认识你姐姐，我们是同学。
wǒ rènshi nǐ jiějie, wǒmen shì tóngxué
I know your sister — we're classmates.
2. Adding 吗 to a statement's embedded question. When 知道 heads a statement ("I know who he is"), the embedded question 他是谁 takes no 吗 — adding it wrongly turns the sentence into a yes/no question.
❌ 我知道他是谁吗。
Wrong — the embedded question in a statement takes no 吗; 吗 would make it a question.
✅ 我知道他是谁。
wǒ zhīdào tā shì shéi
I know who he is.
3. Using 知道 for a skill. "Know how to" is 会, not 知道.
❌ 我知道游泳。
Wrong — knowing how to do something is 会.
✅ 我会游泳。
wǒ huì yóuyǒng
I know how to swim.
4. Using 知道 for 'understand'. Getting the information is 知道了; grasping / comprehending is 懂了 or 明白了.
❌ 老师讲的语法我不知道。
Wrong for 'I don't understand the grammar' — comprehension is 懂 / 明白.
✅ 老师讲的语法我不懂。
lǎoshī jiǎng de yǔfǎ wǒ bù dǒng
I don't understand the grammar the teacher explained.
Key Takeaways
- 知道 = "know a fact / know that…"; it freely takes a clause (我知道他来了) or embedded question.
- An embedded question inside 知道 takes no 吗 — 吗 appears only once, at the sentence end.
- 我知道了 (with 了) = "got it"; bare 我知道 can sound curt.
- English "know" splits four ways: 知道 (fact), 认识 (person), 会 (skill), 懂/明白 (understand).
- 知道 is a state verb — no progressive 在, no reduplication.
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- 认识 (rènshi) — know / recognize (a person)HSK 1 — 认识 (rènshi) is 'be acquainted with, recognize' — a person, a character, or a road you've encountered before. It's one of the several verbs Chinese splits English 'know' into: 认识 (acquainted), 知道 (know a fact), 会 (know how to), 懂 (understand).
- 懂 (dǒng) — to understandHSK 2 — 懂 (dǒng) is 'understand / comprehend' — grasping the content of a language, subject, or situation. It works as a main verb (我懂了) and, very often, as a resultative complement (听懂 'understand by ear', 看懂 'understand by reading'), with ability folded into the potential form 听不懂.