How to Say “Mistakenly Thought” with 以为 (yǐwéi)
以为 (yǐwéi) is the verb for a belief that turned out wrong: Subject + 以为 + [a statement that's actually false]. 我以为他是老师 (“I thought he was a teacher,” but he isn't), 我以为你不来了 (“I thought you weren't coming,” but you did). Unlike neutral “think,” 以为 builds in “… but I was wrong,” so for an opinion you still hold use 觉得 (“I feel / think”) or 认为 (“I hold that”).
Why this trips learners up
English uses “thought” for both right and wrong beliefs, leaving context to tell them apart. Chinese has a dedicated verb for the wrong one: 以为 (yǐwéi), literally “take (以) to be (为).” It frames whatever follows as something you believed but that turned out to be false. The structure is simply Subject + 以为 + [a whole statement]: 我以为他是老师 (“I thought he was a teacher”, he isn't), 我们以为你不在家 (“we thought you weren't home”, you were), 老师以为学生都听懂了 (“the teacher thought the students all understood”, they didn't).
The built-in “but I was wrong” is the whole point, and it's why 以为 shows up so often in the “reveal” moment, when a new fact corrects you: 你们分手了？我以为你们还在一起 (“you broke up? I thought you were still together”), 你去吃辣了？我以为你不爱吃辣 (“you ate spicy food? I thought you didn't like it”). It's usually about the past, but it can describe any time, and it powers the famous rhetorical jab 你以为你是谁？ (“who do you think you are?”) and the warning 不要以为… (“don't go thinking that…”).
Here's the trap. Because English “I thought / I think” feels neutral, learners reach for 以为 when they mean an opinion they still hold, and accidentally say it's wrong. For a present view that may well be right, use 觉得 (juéde, the casual “I feel / I think”) or 认为 (rènwéi, the firmer “I hold / I maintain”). 我觉得你说得对 (“I think you're right”, and I still do) is completely different from 我以为你说得对 (which sounds like “I'd wrongly assumed you were right”).
The three split cleanly. 以为 = a belief now known to be wrong (我以为今天是星期五, “I thought it was Friday”). 觉得 = a casual current opinion or feeling (我觉得很好). 认为 = a considered, firmer judgement, also used for facts and formal statements (科学家认为地球是圆的, “scientists hold that the earth is round”, you'd never use 以为 here, since the belief is correct). A quick test: if you could add “… but actually, no,” it's 以为; if you'd stand by it, it's 觉得 or 认为.
The structure
Colour key
Each colour marks one grammatical role — and the same colour means the same role on every page in the Lab.
Examples in context
Real-world sentences, easiest first. Toggle pinyin or the translation, tap any word to see its role, or play the audio.
Tap a word to see its grammatical role.
wǒ 我 Subject yǐwéi 以为 Pattern tā 他 Subject shì 是 Verb lǎoshī 老师 Object
I thought he was a teacher (but he isn't, the basic 以为).
wǒmen 我们 Subject yǐwéi 以为 Pattern nǐ 你 Subject bù 不 Negation zài jiā 在家 Verb
We thought you weren't home (but you were).
dàjiā 大家 Subject dōu 都 Adverb yǐwéi 以为 Pattern wǒ 我 Subject èrshí suì 二十岁 Verb
Everyone thought I was twenty (a mistaken assumption about age).
lǎoshī 老师 Subject yǐwéi 以为 Pattern xuéshēng 学生 Subject dōu 都 Adverb tīngdǒng 听懂 Verb le 了 Function word
The teacher thought all the students understood (they didn't).
nǐ 你 Subject yǐwéi 以为 Pattern nǐ 你 Subject shì 是 Verb shéi 谁 Question
Who do you think you are? (the rhetorical 你以为你是谁).
bùyào 不要 Negation yǐwéi 以为 Pattern tā 他 Subject shì 是 Verb nǐ de péngyou 你的朋友 Object
Don't go thinking he's your friend (the negative command 不要以为).
nǐmen fēnshǒu le? 你们分手了？ Other wǒ 我 Subject yǐwéi 以为 Pattern nǐmen 你们 Subject hái 还 Adverb zài yìqǐ 在一起 Verb
You broke up? I thought you were still together (the “reveal” use).
wǒ kàndào nà zhāng zhàopiàn 我看到那张照片 Other yǐwéi ，以为 Pattern nǐ 你 Subject yǒu 有 Verb nánpéngyou 男朋友 Object le 了 Function word
I saw that photo and thought you had a boyfriend (an observation that misled me).
Common mistakes
Why it happens: For an opinion you still hold, use 觉得, not 以为. 我觉得你说得对 means “I think you're right” (and I do); 我以为你说得对 sounds like “I'd wrongly assumed you were right.” 以为 always implies the belief turned out false.
Why it happens: When a fact has just corrected you, use 以为, not 觉得. “You're back? I thought you weren't coming till tomorrow” is 我以为你明天才回来, not 我觉得…; 觉得 is a present opinion, while 以为 is the now-corrected assumption the reveal calls for.
Why it happens: For an established fact or firm judgement, use 认为, not 以为. “Scientists hold that the earth is round” is 科学家认为地球是圆的, not 以为, because 以为 would imply the belief is mistaken. Save 以为 for beliefs that turned out wrong.
Compare & contrast
| 以为: thought (but turned out wrong) | 觉得 / 认为: think / believe (could well be right) | The difference |
|---|---|---|
| 我以为今天是星期五wǒ yǐwéi jīntiān shì xīngqīwǔ = “I thought today was Friday” (it isn’t) | 我觉得今天过得很快wǒ juéde jīntiān guò de hěn kuài = “I feel today went by fast” (a view, not wrong) | 我以为今天是星期五 = “I thought today was Friday,” said when you've just learned it isn't. 我觉得今天过得很快 = “I feel today went by fast,” a present impression that isn't wrong. 以为 looks back on a mistake; 觉得 states a current view. |
| 我以为你不来了wǒ yǐwéi nǐ bù lái le = “I thought you weren’t coming” (but you did) | 我认为你应该来wǒ rènwéi nǐ yīnggāi lái = “I believe you should come” (a firm opinion) | 我以为你不来了 = “I thought you weren't coming” (but here you are). 我认为你应该来 = “I believe you should come,” a firm opinion you stand by. 以为 is the assumption that got overturned; 认为 is the judgement you hold. |
Try it yourself
Say “I thought he was a teacher.” Put the mistaken belief as a clause after 以为.
Related patterns
Quick reference card
How to Say “Mistakenly Thought” with 以为 (yǐwéi) grammar.merrymandarin.com A pocket summary — print it and keep it by your desk.