HSK 4
万一⋯⋯，（就）⋯⋯
wàn yī ⋯ ⋯ ， （ jiù ） ⋯ ⋯
The structure 'In case... (then)...' to talk about a possible bad situation
Explanation
万一 (wànyī) is used to introduce a hypothesis about a BAD possibility, one that is unlikely but can still happen, meaning 'in case', 'just in case', 'if by any chance'. This is a type of hypothetical compound sentence (a sentence with a clause stating an assumed condition).
万一 (wànyī) + an assumed bad situation，(就 jiù) + response/consequence. For example 万一我没来，你就自己先去吧 in case I don't come, just go ahead by yourself. The latter clause often has 就 (jiù, then) to introduce the result.
when giving instructions or preparing a contingency plan for a possible risk; it always carries the nuance of something undesirable.
万一 (wànyī) is only used for a BAD and unlikely possibility; whereas 如果 (rúguǒ, if) is neutral, used for any hypothesis, good or bad. When the hypothesis is good or ordinary, use 如果, not 万一.
using 万一 for a good situation (wrongly writing 万一考得好, should use 如果考得好); and remember the latter clause should have 就 to link the result.
Examples
In case I don't come, just go ahead by yourself first.
You must bring your passports; in case they're needed, it'll be a hassle if you don't have them.
Practice
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Learn “万一⋯⋯，（就）⋯⋯” effectively
The grammar point “万一⋯⋯，（就）⋯⋯” (The structure 'In case... (then)...' to talk about a possible bad situation) is one of the key structures at HSK 4. To use it fluently, you need to understand the contexts where it's used and practice regularly.
Study tip: read the examples aloud many times to build a natural reflex. Then try making your own sentences for your own situations. Use the audio button to hear and practice accurate pronunciation.
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