一 + measure + 就 + Verb
Use this when you want to highlight that an action happened almost instantly after a tiny trigger — 'the moment X, Y followed.' The 一 + measure word names the smallest possible unit of the trigger (one look, one sip, one moment), and 就 delivers the consequence with no delay. It is the Chinese workhorse for cause-and-effect that feels immediate and a little inevitable.
Structure
一 [MEASURE/QUANTITY] 就 [VERB]
yī [MEASURE] jiù [VERB]
How to Think About It
This is 一...就... in its quantity-emphasizing form. The measure word turns the trigger into something countably small — '一看就懂' means understanding came after exactly one look, no more needed. Drop the measure word and you get the plain 一...就... pattern (一到家就睡觉). Adding the measure word does one job: it dramatizes how little input was required for the result.
Examples
这道题我一看就会。
zhè dào tí wǒ yí kàn jiù huì.
I knew how to solve this problem the moment I saw it.
他一喝就醉。
tā yì hē jiù zuì.
He gets drunk after a single drink.
孩子一听见妈妈的声音就笑了。
háizi yì tīngjiàn māma de shēngyīn jiù xiào le.
The child smiled the moment he heard his mother's voice.
Common Mistake
Learners add 了 right after 就 because they associate completion with 了. But 就 already carries the sense of 'right then'; piling 了 in between 就 and the verb breaks the rhythm. The 了 belongs at the very end if anywhere, marking the completed event.
他一看就了懂。
他一看就懂了。
Don't Confuse With
一...就...
Same family. Use the plain version (一到家就睡觉) when the trigger is an event; use 一 + measure + 就 (一看就懂) when you want to count how few units of the trigger were needed.
才 + Verb
Opposite feel. 才 = 'only then, finally.' 就 = 'right away, easily.' 一看就懂 means understood instantly; 看了三遍才懂 means understood only after the third look.
立刻 / 马上
These are time adverbs you add to a single clause. 一...就... links TWO clauses — the trigger and the response.
Practice
Fill the blank: 这个字我____看就认识。
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一
Fill the blank: 她一尝____知道是谁做的。
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就
Arrange: 就 / 一 / 我 / 累 / 跑
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我一跑就累。
Translate to Chinese: He understood the moment he heard it.
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他一听就懂。
Write a sentence describing a fast reaction using 一 + measure + 就.
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我一看天气就知道要下雨了。
Hear It in Real Episodes
This pattern appears in 1 Fluentide episode. Press play to hear the sentence:
卖票只用了十八个小时，就全部卖完了。
ticket sales took only eighteen hours, and were all sold out.
HYROX Fitness Race Surges 300% in USElementary
Related Grammar Patterns
Acquire by listening
Hear 一 + measure + 就 + Verb in real Chinese, not in a textbook.
Fluentide picks the next news episode at your level, so this pattern shows up again and again in real context. The transcript marks it, the audio drills it. Free to start.