又 vs 再 (Realized vs Unrealized Repetition) | Chinese (Mandarin) Grammar

English gets by with a single word, "again," for every kind of repetition. Chinese does not — and choosing between 又 (yòu) and 再 (zài) trips up learners more than almost any other adverb pair. The good news is that there is one clean axis behind the choice, and once you see it you can decide correctly every time. 又 is for repetition that is realized — it has already happened, or it habitually recurs. 再 is for repetition that is unrealized — it is still to come: intended, requested, or hypothetical. Get that axis right and the mechanical detail (why 又 loves 了 and 再 refuses it) falls out for free.

The one axis: realized vs unrealized

Don't think "past vs future" — think realized vs unrealized, because it explains the edge cases that the past/future shortcut gets wrong.

	又 (yòu)	再 (zài)
Repetition is…	realized — already occurred / habitual	unrealized — still to come
Typical time	past or recurring present	future, request, command, condition
Sentence-final 了	usually present (又…了)	absent (再 …)
Example	他又来了 — he came again	他明天再来 — he'll come again tomorrow

The label "unrealized" is what makes 再 the word for commands and requests too — when you ask someone to do something again, the second doing hasn't happened yet.

The contrast pairs

The fastest way to internalise the axis is to hold the same verb in both frames and watch the adverb flip:

他又来了，刚坐下。

tā yòu lái le, gāng zuò xià

He came again — he's just sat down. (realized → 又, with 了)

他明天再来，你别担心。

tā míngtiān zài lái, nǐ bié dānxīn

He'll come again tomorrow — don't worry. (unrealized → 再, no 了)

这个笑话你又说了一遍。

zhège xiàohua nǐ yòu shuō le yí biàn

You've told that joke one more time. (it already happened → 又…了)

不好意思，请你再说一遍。

bù hǎoyìsi, qǐng nǐ zài shuō yí biàn

Sorry, could you say that once more? (a request, still to come → 再)

这部电影我又看了一遍，还是很感动。

zhè bù diànyǐng wǒ yòu kàn le yí biàn, háishì hěn gǎndòng

I watched this film one more time — still moving. (realized → 又…了)

这部电影真好，我想再看一遍。

zhè bù diànyǐng zhēn hǎo, wǒ xiǎng zài kàn yí biàn

This film is so good — I want to watch it once more. (intended → 再)

你又迟到了，会已经开始了。

nǐ yòu chídào le, huì yǐjīng kāishǐ le

You're late again — the meeting's already started. (realized → 又…了)

求你了，别再迟到了。

qiú nǐ le, bié zài chídào le

Please, don't be late again. (a plea about the future → 再)

Why 又 takes 了 and 再 doesn't

This is not an arbitrary rule you must memorise separately — it follows directly from the axis. A realized repeat is a completed, actualised event, so the perfective / change-of-state 了 attaches naturally: something new has happened. A 再 repeat, by contrast, has not happened yet, so there is nothing for 了 to mark as realized — attaching 了 would contradict the very meaning of 再. That mechanical difference is your safety check:

我又吃了一个。

wǒ yòu chī le yí ge

I ate one more. — 又 with 了: the eating is done. (informal)

我要再吃一个。

wǒ yào zài chī yí ge

I'm going to eat one more. — 再 without 了: the eating is still to come. (informal)

💡

Use 了 as a lie detector. If a sentence ends in 了 and means "again," the adverb must be 又. If the "again" points at something not yet done — a plan, a request, an order — it's 再, and there is no 了. You almost never see 再…了 meaning "will do again."

The edge case the "past/future" shortcut breaks

Beginners are often taught "又 = past, 再 = future." That works most of the time but fails on a certain, cyclical future — a recurrence that is an established fact of reality rather than a planned action. Because the recurrence is already built into the world, it counts as realized in pattern, and Chinese uses 又:

明天又是星期一了，这个周末过得真快。

míngtiān yòu shì xīngqīyī le, zhège zhōumò guò de zhēn kuài

Tomorrow's Monday again — this weekend went by so fast. (a certain cycle → 又, even though it's future)

一年又过去了，我们又老了一岁。

yì nián yòu guòqù le, wǒmen yòu lǎo le yí suì

Another year has gone by, and we're a year older again. (inevitable recurrence → 又)

The realized/unrealized axis handles this cleanly where "past/future" does not: Monday's arrival isn't something anyone decides to repeat — it just recurs, so it patterns like a realized fact.

Common Mistakes

1. Using 再 for a past repeat. The most frequent form of this error — a repeat that already happened must be 又.

❌ 他昨天再来了。

Incorrect — the visit already happened, so it's 又: 他昨天又来了.

✅ 他昨天又来了。

tā zuótiān yòu lái le

He came again yesterday. — realized repeat → 又…了.

2. Using 又 for a planned future repeat. An intended repeat is unrealized — switch to 再.

❌ 我明天又来。

Incorrect — a planned future repeat is unrealized, so use 再: 我明天再来.

✅ 我明天再来。

wǒ míngtiān zài lái

I'll come again tomorrow. — unrealized repeat → 再, no 了.

3. Adding 了 to 再. Since the 再 event hasn't happened, the realized-event 了 doesn't belong on it.

❌ 我明天再来了。

Incorrect for 'I'll come again' — 再 refers to an unrealized action, so no sentence-final 了.

✅ 我明天再来。

wǒ míngtiān zài lái

I'll come again tomorrow. — no 了 with a still-to-come 再.

4. Using 又 in a request or command. Asking someone to do something again points at the future — that's 再, never 又.

❌ 请又说一遍。

Incorrect — a request is about a not-yet-done action, so use 再: 请再说一遍.

✅ 请再说一遍。

qǐng zài shuō yí biàn

Please say it once more. — a request → 再.

Key Takeaways

Split "again" by realized vs unrealized, not simply past vs future.
又 (yòu): the repeat already happened or habitually recurs — usually with sentence-final 了. See 又 in detail.
再 (zài): the repeat is still to come — future, request, command, condition — and takes no 了.
The 了 partnership is a consequence of the axis, not a separate rule: realized events take 了; unrealized ones can't.
Edge case: a certain cyclical future (明天又是星期一) uses 又, because the recurrence is an established fact of reality, not a plan.

Now practice Chinese

Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.

Start learning Chinese→