A2
一…就… — as soon as
The 一…就 pattern in Chinese for one thing following immediately on another, why both halves need a verb, and how it shades into “whenever”.
一 in front of the first verb and 就 in front of the second says the two events were touching — no gap, no delay.
我一说他就懂了。
Wǒ yì shuō tā jiù dǒng le.
He got it the moment I said it.
他一回家就睡觉了。
Tā yì huí jiā jiù shuìjiào le.
He went straight to bed when he got home.
我一到就给你打电话。
Wǒ yí dào jiù gěi nǐ dǎ diànhuà.
I’ll ring you as soon as I arrive.
The 一 here is not the number. It is doing the same job as English the moment or the instant — and it takes its usual tone changes, yì before most syllables and yí before a fourth tone.
Both halves need a verb
The pattern joins two actions, so a noun on either side will not do.
一雨就不去。
一下雨就不去。
雨 is rain, the thing. 下雨 is raining, the event. 一 needs something that happens.
The subjects can differ
Either one subject doing both things, or two people — and when the subjects differ, each goes in front of its own half.
老师一进来，学生就安静了。
Lǎoshī yí jìnlai, xuésheng jiù ānjìng le.
The students went quiet the moment the teacher walked in.
Note 就 stays in front of its verb and after its subject, which is where it always sits.
It also means “whenever”
Used of something habitual, the pattern stops being about one occasion and becomes a reliable rule about the world. Nothing in the grammar changes; the time frame does the work.
他一喝酒就脸红。
Tā yì hē jiǔ jiù liǎn hóng.
He goes red whenever he drinks.
我一坐车就想睡觉。
Wǒ yí zuò chē jiù xiǎng shuìjiào.
Buses always make me sleepy.
This is the use you will hear most, and it is how a lot of complaints and observations get made in Chinese.
Against 以后
以后 also joins two events, and the difference is the promise of immediacy. 下课以后我回家 is I go home after class, which allows for stopping on the way. 我一下课就回家 says you did not.