Chinese Grammar │了 le

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→ Chinese Grammar│過 guò (1)
→ Difference of「了 le、過 guò」

Introduce：Chinese Grammar │了 le

「了 le」indicates that an verb, action or event was completed ,have taken place , or take place in the future.
Audio of below example sentences (Taiwan accent)

Usage of「了 le」
Difference when 「了 le」exists or non-exists.
e.g. I buy three apples
       我買[买]三個蘋[个苹]果。
       wǒ mǎi sān gè píngguǒ

e.g. I bought three apples
       我買了三個蘋果。
       wǒ mǎi le sān gè píngguǒ

→ the action was completed

When it take place in the future

There is no any difference usage with normal usage.
e.g. After you go to Taiwan, remember to buy a souvenir for me

       你去了台灣後，記得幫我買紀念品。
                     [湾后，记    帮    买纪]
       nǐ qùle táiwān hòu, jìdé bāng wǒ mǎi jìniànpǐn

「記得」means "remember".

「幫」means "help".
「紀念品」means "souvenir".

For persistent verb
There is no any difference usage with normal usage.

e.g. It rains in Taipei

       台北下了雨。

       Táiběi xiàle yǔ

Describe a behavior or event instead of a verb

If you want to describe a behavior or event instead of verb, it should put「了 le」at end of behavior or event.

e.g. It rains in Taipei

       台北下雨了。

       Táiběi xià yǔ le

→ Put「了 le」behind「raining 下雨 xià yǔ」

e.g. I have bought an apple.
       我買蘋果了。

       wǒ mǎi píngguǒ le.

→ Put「了 le」behind「have bought an apple 買蘋果 mǎi píngguǒ」

Without description for time, it may refer three situations below：

It's raining in Taipei.(May keep happening)

It rains in Taipei. (May just happens)

It rained in Taipei. (May happen in the past)

Negative usage

The negation is marked by negation particle「沒 méi/ 沒有 méiyǒu」before the verb and remove「了 le」.
e.g. I didn't buy apples.

       我沒(有)買蘋果。

       wǒ méi (yǒu) mǎi píngguǒ

To ask question

To ask question,「沒 méi/ 沒有 méiyǒu」should be added at end of sentence, or added「嗎[吗] ma」.

e.g. Have you bought an apples?

       你買蘋果了沒(有)?

       nǐ mǎi píngguǒ le méi (yǒu) ?

e.g. Have you bought an apples?

       你買蘋果了嗎?

       nǐ mǎi píngguǒ le ma?

Advanced usage

Usage：When the situation changes, you also can use「了 le」.

If you want to describe a situation changing instead of verb, it should put「了 le」at end of situation .

e.g. I can speak Chinese

       我會說[会说]中文。

       wǒ huì shuō zhōngwén

e.g. I can speak Chinese.

       我會說中文了。
       wǒ huì shuō zhōngwén le

→ I cannot speak Chinese in the past.

→ Put「了 le」behind「can speak Chinese 會說中文 huì shuō zhōngwén」.

Usage：Negative usage for situation changing

The negation is by adding negation particle「不 bù, bú 」in front of the situation.

e.g. I won't buy an apple anymore.

       我不買蘋果了。
       wǒ bù mǎi píngguǒle.

→ I want to buy apple in the past..

→ Put「不 bù, bú 」in front of「buy an apple 買蘋果 mǎi píngguǒ」.

Usage：About to 

「了 le」is often used with adverb「要yào ,快 kuài, 快要 kuài yào」.
It indicates the verb, behavior, or event will is taking place soon.
「了 le」indicates an imminent change of situation.

e.g. It's going to rain.
       快下雨了。
       kuài xià yǔle

       要下雨了。
       yào xià yǔle

       快要下雨了。
       kuàiyào xià yǔle