Not A but B: 不是……而是
复句 / complex sentences
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
(Subject) + 不是 + A，而是 + B
不是A，而是B (bú shì… ér shì…) corrects an idea: "it's not A, it's B". You reject A and assert B instead.
Very useful for giving your opinion or adding nuance: 问题不是钱，而是时间 (the problem isn't money, it's time).
Don't confuse it with 不是A，就是B (either A or B): see the point on 不是……就是.
Examples
我不是不同意，而是还需要考虑一下。
Wǒ bú shì bù tóngyì, ér shì hái xūyào kǎolǜ yíxià.It's not that I disagree: I just need to think it over.
成功的关键不是聪明，而是努力。
Chénggōng de guānjiàn bú shì cōngming, ér shì nǔlì.The key to success isn't intelligence, it's hard work.
他不是我的老师，而是我的同学。
Tā bú shì wǒ de lǎoshī, ér shì wǒ de tóngxué.He's not my teacher, he's my classmate.
Common mistakes
✗ 不是A，但是B → ✓ 不是A，而是B。
✗ 他不是医生，而他是老师。 → 而是 stays together. ✓ 他不是医生，而是老师。