Necessary condition: 只有……才
复句 / complex sentences
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
只有 + condition，(Subject) + 才 + result
只有……才 means "only if… (then)…". The condition is necessary: without it, no result. It stresses difficulty or a requirement.
才 goes after the subject of the second clause, before the verb.
只要早点儿睡，就不会累 (just go to bed early and you won't be tired) ≠ 只有早点儿睡，才不会累 (only going to bed early will keep you from being tired: there's no other way).
Examples
只有坚持锻炼，身体才会健康。
Zhǐyǒu jiānchí duànliàn, shēntǐ cái huì jiànkāng.Only by exercising regularly can you stay healthy.
只有医生同意，你才能出院。
Zhǐyǒu yīshēng tóngyì, nǐ cái néng chūyuàn.You can only leave hospital if the doctor agrees.
只有多听多说，才能学好中文。
Zhǐyǒu duō tīng duō shuō, cái néng xuéhǎo Zhōngwén.Only by listening and speaking a lot can you master Chinese.
Common mistakes
✗ 只有你来，我就高兴。 → 只有 pairs with 才. ✓ 只有你来，我才高兴。
✗ 才 doesn't take a sentence-final 了: ✗ 他十点才来了。 ✓ 他十点才来。