Only if… (只有…才…)

Structure 只有 + necessary condition，才 + result

只有…才… (zhǐyǒu… cái…) marks a NECESSARY condition: ONLY if A happens does B (and no other way). 只有努力学习，才能学好 = "only by studying hard can you learn well". It’s stricter than 只要…就…: there’s no shortcut, A is essential. Note 才 (not 就) in the result.

Examples

只zhǐ有yǒu努nǔ力lì学xué习xí，才cái能néng学xué好hǎo。
Only by studying hard can you learn well.
只zhǐ有yǒu他tā才cái知zhī道dào。
Only he knows.
只zhǐ有yǒu多duō练liàn习xí，才cái能néng进jìn步bù。
Only by practising a lot can you improve.

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