I can't understand the situation when it is better to use them. I don't understand their difference.

  • do you have any example sentences? 一⋯⋯就 ⋯⋯ can be used to mean something happens one after another, but it could be different in other contexts. I can't think of a grammar with 了⋯⋯就⋯⋯, could these be two separate grammar points instead of related? If you have some example sentences, we can help you clearly understand the differences of use.
    – zagrycha
    Jan 23, 2023 at 9:52
  • Perhaps, : 我一写完日记就上床睡觉/ 下课了我就去看电影
    – Tatiana
    Jan 23, 2023 at 10:48

2 Answers 2


我一写完日记就上床睡觉。 this sentence is the grammar I mentioned in my comment, using 一⋯⋯就⋯⋯ to show something is right after another. In this case I would say an english translation could be: I go to bed right after I write in my journal.

下课了我就去看电影。The 了 is a separate grammar point here. 下课 is a verb to get out of class (cause its over) and 了 is serving its common purpose after a verb to show completion. The 就 here means as soon as. So you could translate the sentence: As soon as I am out of class I go to see the movie.

So the two formats you mentioned aren't directly related, and it may not be useful to compare them too closely. If we were to compare them anyway, I would say the first sentence was worded to show "do action 1 then immediately action 2". The second sentence was worded to show "at that time immediately do action 1".

link to a wiki page on the 一⋯⋯就⋯⋯ structure for you. The same page should have links to a variety of other 就 uses as well:



imo most of the time they could be exchanged.

一x就y is similar to x了马上就y, x了就立即y, etc.

一x就y is more on the "immediate" part, emphasizing the speed, reflection, etc.

while x了就y is more on the order, implying that X should be finished in order to start Y. it's common to show one self's laziness by saying "a hard condition happen 了我就 do some hard work". (a hard condition happen 了他才会 do some hard work)

X and Y could be both virtual, or both happened. when it's about something already happened, it sounds like telling a story.

when talking about some plan, mostly we'll use 如果x就y and x了就y, unless it's a plan requiring quick reflection, like a game, a battle or arresting criminal, where 一x就y makes sense.

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