How do you use the grammar particle 了(le)?

了is one of the most commonly encountered grammar particles in the modern Chinese language and also one of the most difficult to grasp. The particle 了 can have many different functions in a sentence. Here are the most basic uses to get you started:

Completed action:

了 can be used after a verb to indicate that the action has been completed. This is the most common use of the particle 了。

For example:

我去了图书馆 - I went to the cinema

我买了一支笔 - I bought a pen

The sentence structure is subject+verb+了+object

Change of state:

了 can also be used to indicate a new situation has arised.

For example:

下雨了 - it's raining (indicating that is wasn't raining before)

你胖了 - you're fat (indicating that you weren't fat before)

Indicating immediacy:

了 can also be used at the end of a sentence to indicate that is something is about to happen. With this use, 了 often corresponds with something else preceding the verb to indicate immediacy, such as '快', '快要' or '就要'

For example:

他快去中國了 - He's going to China very soon

我就要離開我的家了 - I'm just about to leave my house

了 is often wrongly presented as the past tense particle - in fact, it can be used in the past, present and future tenses.

For example,

他吃了飯以後會去圖書館學習 - After he has eaten he will go to the library to study

- in this sentence, the particle 了 is being used to indicate a completed action which will take place in the future