一旦…就… yīdàn… jiù…

一旦…就…（yīdàn… jiù…）means “Once (something happens), then… — a hypothetical or inevitable consequence”. 一旦 introduces a condition that is assumed to happen at some point; 就 in the second clause marks the consequence that will then follow. Formation: 一旦 + 情况/条件，(主语) + 就 + 结果

Once (something happens), then… — a hypothetical or inevitable consequence

HSK5

Formation

一旦 + 情况/条件，(主语) + 就 + 结果

Explanation

一旦 introduces a condition that is assumed to happen at some point; 就 in the second clause marks the consequence that will then follow. It stresses that once the condition is triggered, the result is hard to avoid or reverse. Often used for warnings, rules, or serious consequences. 一旦 can attach to a verb phrase or a whole clause.

Examples

一旦 决定了，就 不能反悔。
yídàn juédìng le, jiù bù néng fǎnhuǐ.
Once you've decided, you can't go back on it.
一旦 养成坏习惯，就 很难改掉。
yídàn yǎngchéng huài xíguàn, jiù hěn nán gǎidiào.
Once you develop a bad habit, it's hard to get rid of.

Note

一旦 is more formal/serious than 如果. The second clause usually needs 就 (or 便).

FAQ

一旦…就… — what does it mean and how is it used?

Once (something happens), then… — a hypothetical or inevitable consequence. 一旦 introduces a condition that is assumed to happen at some point; 就 in the second clause marks the consequence that will then follow. It stresses that once the condition is triggered, the result is hard to avoid or reverse. Often used for warnings, rules, or serious consequences. 一旦 can attach to a verb phrase or a whole clause.

一旦…就… — how do you form it?

一旦 + 情况/条件，(主语) + 就 + 结果

一旦…就… — any usage notes?

一旦 is more formal/serious than 如果. The second clause usually needs 就 (or 便).

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