How to Say “All at Once” with 一下子 (yíxiàzi)
一下子 (yíxiàzi) is a colloquial adverb for “all at once / suddenly / in an instant” — a fast, sharp change in a very short time. Subject + 一下子 + Predicate + 了: 天气一下子变冷了 (“it suddenly turned cold”). Add 就 for “right away / easily” (我一下子就明白了). Because it implies completion, it almost always ends in 了.
Why this trips learners up
一下子 (yíxiàzi) means “all at once / suddenly / in an instant.” It’s a casual, vivid way to say a change happened fast — often a sharp or dramatic one — over a very short stretch of time. The pattern is Subject + 一下子 + Predicate + 了: 天气一下子变冷了 (“the weather suddenly turned cold”), 听到这个消息，我一下子愣住了 (“hearing the news, I froze”). Because 一下子 bakes in a sense of completion, the sentence almost always ends in 了 — leaving it off sounds unfinished.
Add 就 after 一下子 for the “quickly / easily / right away” flavour — 一下子就 + Predicate + 了: 我一下子就明白了 (“I understood all at once”), 孩子一下子就学会了 (“the kid picked it up right away”), 看到妈妈，小孩一下子就不哭了 (“seeing mom, the child stopped crying instantly”). The 就 stresses how smoothly and immediately it happened.
The trap is the shared root with 一下. The post-verb 一下 means “briefly / a bit” — 看一下 (“take a quick look”), 等一下 (“wait a moment”) — and sits after the verb. 一下子 is the opposite: it sits before the predicate and means sudden, not brief. (一下 can stand in for 一下子 in this “suddenly” sense, but the brief-action 一下 is a different job.) So 你站一下 = “stand for a sec,” while 他一下子站起来了 = “he shot up all at once.”
One more thing: 一下子 is an instant, so it clashes with a long duration — 他一下子就学会了 (“learned it in a flash”), never 他一下子学了三年.
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.
fángjiān lǐ 房间里 Place yíxiàzi 一下子 Pattern ānjìng 安静 Adjective le 了 Pattern
The room suddenly went quiet (一下子 + adjective + 了).
tīngdào zhège xiāoxi 听到这个消息 Time wǒ 我 Subject yíxiàzi 一下子 Pattern lèngzhù 愣住 Verb le 了 Pattern
Hearing the news, I froze all at once (一下子 + verb + 了).
wùjià 物价 Subject yíxiàzi 一下子 Pattern zhǎng 涨 Verb le 了 Pattern bù shǎo 不少 Other
Prices suddenly went up quite a bit (一下子 — a sharp change).
yǔ 雨 Subject yíxiàzi 一下子 Pattern xià dà 下大 Verb le 了 Pattern
The rain suddenly got heavy (一下子 + 了).
tā 他 Subject yíxiàzi 一下子 Pattern jiù 就 Adverb cāidào 猜到 Verb dá’àn 答案 Object le 了 Pattern
He guessed the answer right away (一下子就 — quickly / easily).
zhè shǒu gē hěn jiǎndān 这首歌很简单 Time háizi 孩子 Subject yíxiàzi 一下子 Pattern jiù 就 Adverb xuéhuì 学会 Verb le 了 Pattern
This song is easy — the kid learned it in a flash (一下子就…了).
kàndào māma 看到妈妈 Time xiǎohái 小孩 Subject yíxiàzi 一下子 Pattern jiù 就 Adverb bù kū 不哭 Verb le 了 Pattern
Seeing mom, the child stopped crying at once (一下子就不…了).
yōuhuìquàn yì fā chūqù 优惠券一发出去 Time míng’é 名额 Subject yíxiàzi 一下子 Pattern jiù 就 Adverb bèi qiǎng guāng 被抢光 Verb le 了 Pattern
The moment the coupons dropped, the slots got snapped up in an instant (一下子就 + 被).
Common mistakes
Why it happens: 一下子 carries a sense of completion, so the sentence needs 了: 天气一下子变冷了 (“it suddenly turned cold”), not 天气一下子变冷.
Why it happens: 一下子 goes BEFORE the predicate, not after the verb: 大家一下子就安静了 (“everyone went quiet at once”), not 大家安静一下子了. (The post-verb word is the brief-action 一下.)
Why it happens: 一下子 is an instant / sudden change — it clashes with a long duration. It’s 他一下子就学会了 (“learned it in a flash”), not 他一下子学了三年.
Compare & contrast
| 一下子 — “all at once / suddenly” (before the predicate, +了) | 一下 — “briefly / a bit” (after the verb) | The difference |
|---|---|---|
| 他一下子站起来了tā yíxiàzi zhàn qǐlái le | 你站一下nǐ zhàn yíxià | 他一下子站起来了 = “he shot up all at once” (sudden — before the predicate). 你站一下 = “stand up for a moment” (brief — after the verb). |
| 我一下子就明白了wǒ yíxiàzi jiù míngbai le | 让我想一下ràng wǒ xiǎng yíxià | 我一下子就明白了 = “I got it all at once.” 让我想一下 = “let me think for a sec.” Same 一下 root, opposite position and meaning. |
Try it yourself
Say “The light suddenly went out.” — Subject + 一下子 + verb + 了.
Related patterns
Quick reference card
How to Say “All at Once” with 一下子 (yíxiàzi) grammar.merrymandarin.com A pocket summary — print it and keep it by your desk.