除非…才/否则…: unless / only if
复句 / complex sentences
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
除非 + condition，S 才 + V | 除非 + condition，否则 + consequence
除非 sets a single, indispensable condition. Two constructions with close meaning:
1. 除非 A，才 B: "B only if A" (≈ 只有 A 才 B).
2. 除非 A，否则 B: "unless A, B", B is what happens if A does not.
Mind the logic: with 否则, the second part describes the bad outcome, just like English "unless you invite him, he won't come".
Examples
除非你亲自去请他，他才会来。
Chúfēi nǐ qīnzì qù qǐng tā, tā cái huì lái.He'll only come if you invite him in person.
除非老板同意，否则我们不能改计划。
Chúfēi lǎobǎn tóngyì, fǒuzé wǒmen bù néng gǎi jìhuà.Unless the boss agrees, we can't change the plan.
除非有特别的事，否则他从来不请假。
Chúfēi yǒu tèbié de shì, fǒuzé tā cónglái bù qǐngjià.Unless something special comes up, he never takes leave.
Common mistakes
✗ 除非你去请他，他就会来。 → with 除非 use 才 (or 否则), not 就.
✗ 除非老板同意，否则我们能改计划。 → wrong logic: 否则 introduces what happens without the condition → ✓ 否则我们不能改。