X 不是 ... 是 ...
Reach for this when you want to correct an assumption on the spot — knock down what someone thinks, then state what's actually true. It is the verbal equivalent of 'no, not that — this.' The two halves usually share a subject and contrast two specific things: a wrong label vs. a right one, a fake vs. the real thing, the topic the listener expects vs. the one the speaker actually has in mind.
Structure
[SUBJECT] 不是 [WRONG] ，是 [RIGHT]
bú shì... shì...
How to Think About It
Both halves use 是 because they are both identification claims — you are negating one label and asserting another. The structure works only when the two slots are comparable nouns or noun-like phrases (not actions): you can swap 苹果 for 橘子, but not 高 for 矮. If the contrast is about doing instead of being, you switch to 不是...而是... or rephrase with verbs.
Examples
他不是我哥哥，是我弟弟。
Tā bú shì wǒ gēge, shì wǒ dìdi.
He isn't my older brother, he's my younger brother.
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.
这个问题不是钱的问题，是时间的问题。
Zhège wèntí bú shì qián de wèntí, shì shíjiān de wèntí.
This isn't a money problem, it's a time problem.
Common Mistake
Learners drop the second 是 because in English 'It's not A, B' sounds workable. In Chinese the second 是 is mandatory — without it the listener hears a fragment, not a correction.
这不是茶，咖啡。
这不是茶，是咖啡。
Don't Confuse With
不是...而是...
More formal and slightly stronger. 而是 makes the correction feel argumentative and is preferred in writing or essays; bare 是 is the spoken default.
是...不是...
Same two slots, flipped order. Start with the truth and then knock down the wrong guess. Use it when you want the correct answer to land first.
不是...就是...
Looks similar but means 'if not A, then B' — one of two possibilities is true. Totally different logic: alternatives, not correction.
Practice
她 ___ 老师，是学生。
Show answer
不是
我不是中国人，___ 美国人。
Show answer
是
Put in order: [是 / 这 / 不是 / 茶 / 咖啡]
Show answer
这不是茶，是咖啡。
Translate to Chinese: 'This isn't his car, it's his sister's.'
Show answer
这不是他的车，是他姐姐的。
Correct a wrong guess about your hometown using 不是...是...
Show answer
Example answer: 我不是北京人，是上海人。 (I'm not from Beijing, I'm from Shanghai.)
Hear It in Real Episodes
This pattern appears in 2 Fluentide episodes: