Conjunction 一...就

This pattern links two events. The first event is the trigger. The second event is the immediate result or the next step. The word 一 represents the first action. The word 就 marks the second action. Usually, 就 acts as an adverb meaning "then" or "right away." Together, they create a "Condition + Result" structure. If the first thing happens, the second thing follows instantly. It can describe a single event that happened yesterday. It can also describe a habit you do every morning. It even works for future plans. It is like a verbal bridge between two points in time. The gap between these points is tiny.

1. 1There are two main ways to build this sentence. It depends on how many people are involved.
2. 2For one person doing both things:
3. 3Subject + 一 + Verb 1 + 就 + Verb 2
4. 4Example: 我一喝咖啡就开心 (I am happy as soon as I drink coffee).
5. 5For two different people or things:
6. 6Subject 1 + 一 + Verb 1, Subject 2 + 就 + Verb 2
7. 7Example: 爸爸一回来我们就吃饭 (As soon as Dad returns, we eat).
8. 8Notice where 就 sits. It always comes after the second subject. It stays right before the second verb. Think of 就 as a magnet stuck to the second action. It never starts a sentence. It needs a subject or a verb to lean on.

Use this when Action B follows Action A without any waiting.

• Daily Habits: Use it for your routines. "I check my phone as soon as I wake up."
• Immediate Reactions: Use it for feelings. "I get nervous as soon as the teacher looks at me."
• Fast Sequences: Use it for instructions. "Turn left as soon as you see the bank."
• Logical Results: Use it for cause and effect. "As soon as it rains, the ground gets wet."

Imagine you are at a job interview. The interviewer asks when you can start. You might say, "I can start as soon as I finish my current project." This shows you are efficient. Or imagine you are ordering food. You tell the waiter, "Please bring the bill as soon as we finish eating." It sounds polite and clear. It shows you know exactly what comes next.

Do not use this if there is a long break between actions. If you eat breakfast at 8 AM and lunch at 1 PM, do not use 一...就. That is too slow! Use 然后 (afterwards) instead. Also, avoid using it for things that are not related. If you happen to buy a cat and then the stock market crashes, they probably aren't linked. 一...就 implies a connection or a trigger. If there is no "snap" feeling, stick to simple sequence words. This grammar is for the fast and the furious, not the slow and the steady.

• Forgetting the 就: This is the most common error. You cannot just say 我一去, 睡觉. You must say 我一去就睡觉. Without 就, the sentence feels unfinished. It is like a cliffhanger no one asked for.
• Putting 就 before the subject: Many people try to say 一... 就我.... Nope! The subject must come first. Say 我就... not 就我.
• Double 一: You only need one 一 at the start of the first action. Do not put it before the second action.
• Misplacing 一: Make sure 一 is right before the verb or after the first subject. Don't hide it at the end of the phrase.

Wait, doesn't 以后 (after) mean the same thing? Not quite. 以后 is broad. It could mean five minutes later or five years later. 一...就 is immediate. It's the difference between "After I graduate, I will travel" and "The second I graduate, I’m out of here!"

What about 然后? 然后 is just a list. "I did this, then I did that." It doesn't emphasize speed. 一...就 emphasizes that the first action *caused* or *triggered* the second one right away. It is much more energetic than a simple list.