Saying 'for X amount of time' — and the V了…了 sandwich
Mandarin marks DURATION (a stretch of time) differently from POINTS (a moment in time). Duration phrases like 三天 (three days), 两个小时 (two hours), 一个月 (a month), 五年 (five years) sit AFTER the verb, not before. The trickiest pattern is the 了-sandwich: V + 了 + duration + 了 signals 'have been V-ing for X (and still going)', while V + 了 + duration signals 'V-ed for X (and stopped)'. Stack with 已经...了 (already) and 还没... (haven't yet) to talk about ongoing states. This contrasts with POINT-IN-TIME phrasing — 在 + time for a specific moment vs. 从...到... for a span. Master this layer and you can finally say 'I've been studying Chinese for three years' without circling around it.
Duration phrases — placement after the verb
A Mandarin duration phrase = NUMBER + measure + time-noun. Common ones: 一个小时 = an hour. 两个小时 = two hours. 半个小时 = half an hour. 三天 = three days (note: 天 takes no measure). 一个星期 = a week. 两个月 = two months. 三年 = three years (note: 年 takes no measure). The PLACEMENT is the tricky bit. For an INTRANSITIVE verb (no object): V + duration. 我睡了八个小时。 = I slept for 8 hours. 我等了二十分钟。 = I waited for 20 minutes. For a TRANSITIVE verb with an object, you must REPEAT the verb or use 的 restructure: 我学中文学了三年。 = I studied Chinese for three years (the verb 学 repeats). Or: 我学了三年(的)中文。 = I studied Chinese for three years (duration sits between V+了 and the object, with optional 的). Both are correct; the 'V-O-V-duration' pattern is more conversational. Don't say 我学中文三年 — duration MUST sit in a verb-attached slot.
V + 了 + duration (V-ed for X — completed and stopped)
V + 了 + duration describes a finished stretch — you V-ed for some time, then stopped. 昨天我学了三个小时。 = Yesterday I studied for three hours (and stopped). 我等了你一个小时。 = I waited for you for an hour (and the wait is over). The single 了 after the verb is perfective — it caps the action. Without context, V了 + duration typically means 'did it for that long, no longer doing'. With a topic time like 昨天 or 上个月, this reading is forced. 他昨天工作了八个小时。 = He worked for 8 hours yesterday. The 了 here is the same perfective 了 from lesson 12. Note: putting an additional 了 at the end (the sentence-final 了) changes the meaning to ongoing — see next section.
V + 了 + duration + 了 (have been V-ing for X — still ongoing)
Add a SECOND 了 at the end and the sentence flips to mean 'have been V-ing for X and STILL AM'. 我学中文学了三年了。 = I've been studying Chinese for three years (and I still am). 我等了你一个小时了。 = I've been waiting for you for an hour (and I'm still waiting). 我们认识十年了。 = We've known each other for ten years. The first 了 marks completion-up-to-now; the second 了 is the sentence-final 了 of changed state — it asserts 'as of now'. Together they yield the English perfect progressive. Compare carefully: 学了三年 = studied for three years (done). 学了三年了 = have been studying for three years (still going). The difference is exactly that final 了. Without a duration phrase, 学了 alone just means 'studied / have studied' — context decides whether ongoing. The 了-sandwich is the unambiguous way to signal 'still happening'.
已经 + V + 了 — already V-ed
已经 yǐjīng = already. Pairs naturally with the sentence-final 了 of changed state. 我已经吃了。 = I've already eaten. 他已经走了。 = He's already left. 已经 signals 'before now / earlier than expected'. Stacks with duration: 我已经学了三年中文了。 = I've already been studying Chinese for three years. 他已经在北京住了五年了。 = He's already been living in Beijing for five years. The pattern is 已经 + V + 了 + (duration) + 了 — the sentence-final 了 stays. 已经 also fits with adjectives: 已经晚了。 = It's already late. 天已经黑了。 = The sky has already gone dark. Negation: 还没 (see next section) is the natural opposite — 'not yet'.
还没 + V — haven't yet V-ed
还没 hái méi = 'not yet / haven't [done] yet'. The opposite of 已经...了. 我还没吃。 = I haven't eaten yet. 他还没来。 = He hasn't come yet. 我还没学过那个。 = I haven't studied that yet. Note that 还没 uses 没 (not 不) because we're negating completion / experience. Don't add 了 to the negative: 我还没吃了 is wrong — 了 is for the affirmative completion / change. With duration: 我还没学三年。 = I haven't (yet) been studying for three years (still under three). 他还没工作两个月。 = He hasn't worked two months yet. Add 呢 at the end for a softening / 'still in progress' feel: 我还没吃饭呢。 = I haven't eaten yet (currently still hungry). 还没...呢 is highly natural in conversation.
Specific points vs. spans — 在 vs. 从…到…
POINT-IN-TIME prepositions are different from DURATION phrases. 在 + time = at / on (a specific time): 在三点 = at 3 o'clock. 在星期一 = on Monday. 在2020年 = in 2020. 在 + time sits BEFORE the verb. 我在三点回家。 = I went home at 3. 从 + time + 到 + time = from X to Y (a span with start and end): 从早上八点到下午五点。 = From 8 AM to 5 PM. 我从星期一到星期五上班。 = I work Monday to Friday. 从 + time + 起 = starting from time: 从明天起 = starting tomorrow. 从...开始 = starting from X. The 在 / 从…到… distinction matches English 'at vs. from-to'. With duration, you don't need 在 / 从...到... — you just say the duration phrase: 我学了三年。 = I studied for three years (no preposition). Mixing them is wrong: 我在三年学了 is gibberish.
Common patterns and traps
多长时间? = How long? — the question form. 你学了多长时间? = How long have you been studying? 多久? duōjiǔ = same meaning, slightly more conversational. 你来了多久? = How long have you been here? Both expect a duration as answer. Trap 1: 'I've lived in Beijing for five years' — say 我在北京住了五年了 (with both 了s for ongoing) or 我在北京住了五年 (5 years and now I've left). Choose by truth. Trap 2: don't translate English 'for' literally — there's NO preposition in Mandarin duration; the duration just sits after the verb. 为三年 is wrong. Trap 3: when there's both a place and a duration, place goes first: 我在北京住了五年了。 = I've lived in Beijing for 5 years (place 在北京 before V + duration). Trap 4: 半 + 个 + 小时 (half an hour) but 一个 + 半 + 小时 (1.5 hours) — 半's position changes the meaning.
