了
Pattern
Verb + 了 + object
Key words
Core idea
Completed-action 了 marks an action as complete in the situation being described. It is not a simple past-tense ending.
The key idea is boundedness: the action is presented as done, often with an object, amount, or event boundary.
Not the same as past tense
Do not attach 了 to every past-time sentence. Habits, states, and background descriptions often do not need it, even when English uses past tense.
In ordinary negative completed-action sentences, verbal 了 disappears and the verb is negated with 没.
For questions about whether an action has been completed, Mandarin can ask with a sentence-final completion check such as 没有. That is different from simply adding a yes/no particle to every sentence.
Mini decision rule
Ask whether the sentence presents one action as completed in this situation. If the sentence is about a habit, a general truth, or an event that did not happen, completed-action 了 is usually not the tool you want.
Examples
我买了三张票。
Wǒ mǎi le sān zhāng piào.
I bought three tickets.
了 marks the buying as completed.
她喝了咖啡。
Tā hē le kāfēi.
She drank coffee.
我们看了那部电影。
Wǒmen kàn le nà bù diànyǐng.
We watched that movie.
Common mistakes
Avoid
我昨天了买票。
Use
我昨天买了票。
了 follows the verb, not the time word.
Avoid
我每天喝了咖啡。
Use
我每天喝咖啡。
Habitual actions usually do not need completed-action 了.
Seen in stories
The Accidental Livestream
公司培训刚开始，实习生赵明不小心打开了直播。
Just as the company training began, intern Zhao Ming accidentally turned on a livestream.
The Accidental Livestream
经理没有慌着关掉，而是先让大家确认是否露出了客户信息。
The manager did not rush to shut it off; instead, she first had everyone confirm whether any client information had appeared on screen.
The Comment Section Plan
清单一贴出来，连最爱吐槽的同事都点了赞。
As soon as the checklist was posted, even the coworker who loved complaining most gave it a like.
The Group Chat Apology
第二天，快递员在群里发了一段语音道歉。
The next day, the courier sent a voice apology in the group chat.
The Group Chat Apology
男孩为了感谢大家，带猫拍了一张“失而复得”的照片。
To thank everyone, the boy brought the cat and took a “lost and found” photo.
Show 5 more story examples
The Rooftop Key
台风前一天，公寓管委会发现顶楼钥匙不见了。
The day before the typhoon, the apartment management committee discovered that the rooftop key was missing.
The Rooftop Bento Party
台风过后，顶楼没有漏水，倒是多了一张纸条。
After the typhoon, the rooftop had no leaks, but there was an extra note.
The Rooftop Bento Party
有人带咸酥鸡，有人带珍珠奶茶，连平常最安静的住户都带了水果。
Some people brought salty crispy chicken, some brought bubble tea, and even the usually quiet resident brought fruit.
The Rooftop Bento Party
他下班后真的骑机车来了，还不好意思地说：“我只是怕饭变冷。”
After work he really rode his scooter over and said shyly, “I was only afraid the meal would get cold.”
The Wrong Locker Code
林悦只好把猫粮放在物业前台，还写了一张说明。
Lin Yue had no choice but to leave the cat food at the property desk and write a note.