Does 了 Mean Past Tense? The Completed-Action 了
No — 了 marks completion (aspect), not past tense. Right after a verb it says the action is finished: 我买了 (“I('ve) bought it”), 我吃了三个 (“I ate three”). It works in future sentences too.
Why this trips learners up
Almost every learner's first theory is that 了 (le) is the Chinese past tense — and it's a trap. 了 marks completion (aspect), not when something happened (tense). Sitting right after the verb, it says the action is finished: 我买了 = “I('ve) bought it”, 飞机起飞了 = “the plane has taken off”. The give-away that it isn't past tense: 了 turns up in future sentences too — 我吃了饭就去 = “I'll go once I've eaten”.
Placement has a few cases. Bare: Subject + Verb + 了 (他们到了 = “they've arrived”). With a counted object, 了 sits between the verb and the object: Verb + 了 + [Number + Measure] + Object (我喝了一杯水). A time word works the same way (昨天我看了一部电影), and sometimes 了 goes after the object instead (我交学费了). For a string of actions you use just one 了, after the final verb (我去图书馆借了书) — not one per verb like English. And the negative drops it entirely: “I didn't buy it” is 我没买, never 我没买了. This is the completed-action 了 (了1); for the other one — the 了 at the very end that signals a new situation — see the change-of-state 了.
The structure
Colour key
Each colour marks one grammatical role — and the same colour means the same role on every page in the Lab.
Examples in context
Real-world sentences, easiest first. Toggle pinyin or the translation, tap any word to see its role, or play the audio.
Tap a word to see its grammatical role.
fēijī 飞机 Subject qǐfēi 起飞 Verb le 了 Pattern
The plane has taken off.
kèrén 客人 Subject dōu 都 Adverb dào 到 Verb le 了 Pattern
The guests have all arrived.
wǒ 我 Subject hē 喝 Verb le 了 Pattern yì 一 Number bēi 杯 Measure word shuǐ 水 Object
I drank a glass of water.
zuótiān 昨天 Time wǒ 我 Subject kàn 看 Verb le 了 Pattern yí 一 Number bù 部 Measure word diànyǐng 电影 Object
Yesterday I watched a movie.
wǒ 我 Subject jiāo 交 Verb xuéfèi 学费 Object le 了 Pattern
I('ve) paid the tuition.
zuótiān 昨天 Time wǒ 我 Subject méi 没 Negation qù 去 Verb shàngbān 上班 Verb
I didn't go to work yesterday (the negative drops 了).
wǒ 我 Subject qù 去 Verb túshūguǎn 图书馆 Place jiè 借 Verb le 了 Pattern yì 一 Number běn 本 Measure word shū 书 Object
I went to the library and borrowed a book (one 了, for the whole sequence).
wǒ 我 Subject chī 吃 Verb le 了 Pattern fàn 饭 Object jiù 就 Adverb qù 去 Verb
I'll go once I've eaten — completion in the future, so 了 can't be “past tense”.
Common mistakes
Why it happens: The negative of a completed action is 没 + verb, with NO 了. 没 already says it didn't happen, so the completion 了 drops out: “I didn't buy it” is 我没买, never 我没买了.
Why it happens: 了 marks a one-off completed action, so it clashes with a habit. “I drink coffee every day” is 我每天喝咖啡 (no 了); add 了 and it implies a single finished event, which 每天 contradicts.
Why it happens: A run of actions needs only ONE 了, after the last verb — not one per verb the way English marks every past tense. “I went to the store and bought things” is 我去商店买了东西, not 我去了商店买了东西.
Compare & contrast
| 了 in a PAST sentence | 了 in a FUTURE sentence (still not “past tense”) | The difference |
|---|---|---|
| 我昨天吃了饭。wǒ zuótiān chī le fàn. = I ate (past) | 我明天吃了饭就去。wǒ míngtiān chī le fàn jiù qù. = tomorrow, after I eat (future) | 我昨天吃了饭 — 了 after a past action (“I ate”). 我明天吃了饭就去 — the same 了, in a sentence about tomorrow (“once I've eaten, I'll go”). The 了 didn't change; only 昨天 / 明天 sets the time. |
| 他上周到了。tā shàng zhōu dào le. = he arrived last week | 他到了就给你打电话。tā dào le jiù gěi nǐ dǎ diànhuà. = he'll call once he arrives (future) | 他上周到了 — “he arrived last week” (past). 他到了就给你打电话 — “he'll call once he arrives” (future). Completion either way; the time comes from elsewhere. |
Try it yourself
Say “I drank two bottles of water” — tap the words into order.
Related patterns
Quick reference card
Does 了 Mean Past Tense? The Completed-Action 了 grammar.merrymandarin.com A pocket summary — print it and keep it by your desk.