Since, Otherwise, What If, Once and Unless: 既然, 否则, 万一, 一旦, 除非

既然…就: since (given that)

既然 (jìrán) starts from something both speakers already know, and the main clause draws the obvious conclusion, often a suggestion: 既然你病了，就别去上班了 (since you're ill, don't go to work). English 'since' can be about time or reason; 既然 is only about reason, and only for facts already established.

Compare 因为 (yīnwèi), which gives new information as a cause. 既然 says 'we both know this, so…'.

• 既然你已经决定了，我就不多说了。

  Jìrán nǐ yǐjīng juédìng le, wǒ jiù bù duō shuō le.

  Since you've already made up your mind, I won't say any more.

• 既然来了，就多住几天吧。

  Jìrán lái le, jiù duō zhù jǐ tiān ba.

  Since you're here, stay a few more days.

否则 and 不然: otherwise

否则 (fǒuzé) and 不然 (bùrán) open the second clause and mean 'otherwise, or else'. The first clause is usually advice or a necessity: 快走吧，不然要迟到了 (let's hurry, or we'll be late). 不然 is everyday speech; 否则 is more formal and common in writing and instructions.

Unlike English 'otherwise', these always begin their clause, before any subject.

• 请提前两个小时到机场，否则可能赶不上飞机。

  Qǐng tíqián liǎng ge xiǎoshí dào jīchǎng, fǒuzé kěnéng gǎn bu shàng fēijī.

  Please get to the airport two hours early, otherwise you may miss your flight.

• 多穿点儿，不然会感冒的。

  Duō chuān diǎnr, bùrán huì gǎnmào de.

  Wear something warmer, or you'll catch a cold.

万一, 假如, 一旦…就 and 除非…才

万一 (wànyī, literally 'one in ten thousand') is 'what if, in case': something unlikely and almost always unwelcome. 万一航班取消了怎么办？ (what if the flight is cancelled?). It also gives the reason for a precaution, with the precaution first: 带把伞吧，万一下雨呢？ (take an umbrella, just in case it rains). 假如 (jiǎrú) is a more bookish 如果 for an imagined situation (假如我是你, if I were you); it has no 'just in case' sense.

一旦 (yídàn) means 'once, the moment that': as soon as A happens, B follows, usually something serious. 一旦…就 is common in warnings and rules.

除非 (chúfēi) names the only condition: 除非 A，才 B (only if A, then B) or 除非 A，否则/不然 B (unless A, B). Learners often translate 'unless' with 除非 and forget the second half.

• 万一下雨了，我们就在家看电影。

  Wànyī xià yǔ le, wǒmen jiù zài jiā kàn diànyǐng.

  If it happens to rain, we'll stay in and watch a film.

• 多带点儿钱，万一不够呢？

  Duō dài diǎnr qián, wànyī bú gòu ne?

  Take a bit more money, in case it's not enough.

• 护照一旦丢了，就很麻烦。

  Hùzhào yídàn diū le, jiù hěn máfan.

  Once you lose your passport, it's a real headache.

• 除非你亲自去，他才会同意。

  Chúfēi nǐ qīnzì qù, tā cái huì tóngyì.

  He'll only agree if you go in person.

• 除非有特殊情况，否则不能退票。

  Chúfēi yǒu tèshū qíngkuàng, fǒuzé bù néng tuì piào.

  Unless there are special circumstances, tickets can't be refunded.

Common mistakes

• ✗除非你去，他不会同意。

  ✓除非你去，否则他不会同意。

  Chúfēi nǐ qù, fǒuzé tā bú huì tóngyì.

  除非 needs a partner: 否则 / 不然 before a negative result, or 才 before a positive one (除非你去，他才会同意).

• ✗万一你考上了大学，我们就去旅行。

  ✓要是你考上了大学，我们就去旅行。

  Yàoshi nǐ kǎoshàngle dàxué, wǒmen jiù qù lǚxíng.

  万一 is for something unlikely and almost always unwelcome ('if, heaven forbid'), so with good news it sounds like a joke or a worry. For an ordinary hoped-for event, use 要是 or 如果, like English plain 'if'.

• ✗你快点儿，我们否则会迟到。

  ✓你快点儿，否则我们会迟到。

  Nǐ kuài diǎnr, fǒuzé wǒmen huì chídào.

  否则 and 不然 are conjunctions: they open the clause, before the subject.

Questions learners ask

Related grammar guides

• Even If and No Matter What: 即使…也, 不管…都, 哪怕…也, 再…也 · Upper-Intermediate Chinese
• And So, In the End, Luckily, No Wonder: 于是, 结果, 幸亏, 难怪 · Upper-Intermediate Chinese