Most potential complements pin down a specific result — 看得懂 (can read-and-understand), 拿得动 (can lift). 得了 / 不了 is the broad one: it says an action simply can or can't be brought off, whatever "brought off" means in context — reaching a place, finishing a quantity, enduring a feeling. 去不了 is "can't make it," 吃不了 is "can't manage it all," 受不了 is "can't stand it." The single most important thing to fix in your head: this 了 is not the aspect particle le you already know — it is read liǎo and means "finish, settle, bring to a conclusion." Once you hear it as liǎo, the whole pattern stops looking like a stray 了 and starts making sense.
The 了 here is liǎo — "bring it off"
The character 了 has two lives. As the everyday aspect particle it is toneless le (吃了 chī le, "ate"). But there is an older verb 了 (liǎo) meaning "to finish, to conclude, to be able to settle" — the same liǎo you meet in 了解 (liǎojiě, "to understand thoroughly") and 没完没了 (méi wán méi liǎo, "endless"). It is this liǎo that sits inside the potential complement. So V得了 = "the action can be carried through," and V不了 = "the action can't be carried through."
我今天太忙，去不了。
wǒ jīntiān tài máng, qù bu liǎo
I'm too busy today, I can't make it. (informal) — 去不了, the action 'go' can't be brought off.
这么多菜，我一个人吃不了。
zhème duō cài, wǒ yí ge rén chī bu liǎo
This is way too much food for me to manage on my own. (informal) — capacity is exceeded, so 吃不了.
Forming 得了 and 不了
The frame is dead simple — verb, then 得了 for "can," 不了 for "can't." There is no separate result morpheme to memorise, which is exactly why this pattern is so useful when you don't know (or don't need) a more specific complement.
| Verb | 得了 (can) | 不了 (can't) | Sense of the pair |
|---|---|---|---|
| 去 (qù) | 去得了 (qù de liǎo) | 去不了 (qù bu liǎo) | make it / show up |
| 吃 (chī) | 吃得了 (chī de liǎo) | 吃不了 (chī bu liǎo) | manage to eat it all |
| 忘 (wàng) | 忘得了 (wàng de liǎo) | 忘不了 (wàng bu liǎo) | be able to forget |
| 受 (shòu) | 受得了 (shòu de liǎo) | 受不了 (shòu bu liǎo) | bear / stand |
| 赶 (gǎn) | 赶得了 (gǎn de liǎo) | 赶不了 (gǎn bu liǎo) | catch (in time) |
To ask a yes-no question, use the A-not-A shape of the whole complement: V得了 V不了. This is far more idiomatic than tacking 吗 on the end.
这些菜你一个人吃得了吃不了？
zhèxiē cài nǐ yí ge rén chī de liǎo chī bu liǎo?
Can you finish all these dishes by yourself? (informal) — A-not-A: 吃得了吃不了.
再不走就赶不了火车了。
zài bù zǒu jiù gǎn bu liǎo huǒchē le
If we don't leave now we won't be able to catch the train. (neutral) — 赶不了, plus a genuine sentence-final le.
Notice the last example carries both 了 readings: 赶不了火车 is liǎo (the complement), while the 了 at the very end is the ordinary sentence-final le marking a changed situation.
吃不了 vs 吃不完: capacity vs completion
Learners constantly collide 吃不了 (chī bu liǎo) with 吃不完 (chī bu wán). Both come out as "can't finish it" in English, and in many situations either works — but they profile different things. 了 (liǎo) stresses capacity: the amount is beyond what you can take on. 完 (wán) stresses the endpoint: the process can't be run all the way to its conclusion. (For 完 itself, see the resultative 完 page.)
这么多菜，我实在吃不了。
zhème duō cài, wǒ shízài chī bu liǎo
Honestly, this is more food than I can handle. (informal) — my capacity is the issue: 吃不了.
菜太多了，我们今天肯定吃不完。
cài tài duō le, wǒmen jīntiān kěndìng chī bu wán
There's too much food — we definitely won't finish it today. (informal) — reaching the endpoint is the issue: 吃不完.
A quick test: if you could say "I can't take on that much," reach for 了; if you mean "the job won't get all the way done," reach for 完. With people who ate part of a huge meal, 吃不了 (couldn't take it all on) is usually the more natural choice.
Fixed favourites: 受不了, 大不了, 少不了, 忘不了
Several V不了 combinations have hardened into everyday idioms you should simply know as units.
太吵了，我快受不了了。
tài chǎo le, wǒ kuài shòu bu liǎo le
It's so noisy — I'm about to lose it. (informal) — 受不了, 'can't bear it', is extremely high-frequency.
别担心，大不了从头再来。
bié dānxīn, dà bu liǎo cóngtóu zài lái
Don't worry — worst case, we just start over. (informal) — 大不了 has frozen into an adverb meaning 'at worst / no big deal'.
过年餐桌上少不了一条鱼。
guònián cānzhuō shang shǎo bu liǎo yì tiáo yú
A New Year's table can't do without a fish. (neutral) — 少不了, 'can't be dispensed with / is a must'.
那年夏天的事，我一辈子也忘不了。
nà nián xiàtiān de shì, wǒ yíbèizi yě wàng bu liǎo
What happened that summer — I'll never be able to forget it. (slightly literary) — 忘不了, 'unable to forget'.
Note that 大不了 barely has a live positive counterpart in this idiomatic sense; treat it as a fossilised adverb, not a free V得了/不了 pair. The others (受, 少, 忘) do pair up normally: 受得了, 少得了, 忘得了.
Common Mistakes
1. Reading the 了 as le instead of liǎo. The complement 了 is the verb liǎo ("bring off"), third tone — not the aspect particle.
❌ 我去不了 (read: wǒ qù bu le)
Wrong reading — the 了 here is liǎo, not le.
✅ 我去不了。
wǒ qù bu liǎo
I can't make it. — 不了 is read bu liǎo.
2. Using 不了 when you specifically mean 'reach the endpoint'. For "can't finish (to completion)," 不完 is often sharper than 不了.
❌ 这本书太厚了，一个星期我看不了。
Odd — for 'can't finish reading it' use 看不完; 看不了 suggests you can't read it at all.
✅ 这本书太厚了，一个星期我看不完。
zhè běn shū tài hòu le, yí ge xīngqī wǒ kàn bu wán
This book is so thick I can't finish it in a week. — 看不完 = can't reach the end.
3. Adding a redundant 能 in front. V不了 already means "can't"; stacking 不能 on top is contradictory.
❌ 我今天不能去不了。
Wrong — 去不了 already means 'can't go'; drop the 不能.
✅ 我今天去不了。
wǒ jīntiān qù bu liǎo
I can't make it today. — one negation is enough.
4. Writing 二 instead of the counting numeral, or misplacing the object. The object normally sits before the verb-complement block (this-much-food, I 吃不了) rather than jammed between 得/不 and 了.
❌ 我吃不了这两个了饭。
Wrong — 了 belongs to the complement, not after the object; and don't split 吃不了.
✅ 这两碗饭我吃不了。
zhè liǎng wǎn fàn wǒ chī bu liǎo
I can't manage these two bowls of rice. — object fronted, 吃不了 kept intact, 两 not 二.
Key Takeaways
- 得了 / 不了 (de liǎo / bu liǎo) is the general-purpose potential complement: "can / can't bring the action off."
- The 了 is read liǎo ("finish, settle") — never the toneless aspect particle le.
- Ask yes-no questions with A-not-A: 吃得了吃不了？
- 了 = capacity, 完 = endpoint. 吃不了 (too much for me) vs 吃不完 (can't reach the end).
- Learn the frozen idioms as units: 受不了 (can't stand it), 大不了 (at worst), 少不了 (can't do without), 忘不了 (can't forget).
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- Frozen Potential Idioms: 来不及, 受不了HSK 4 — A handful of potentials have frozen into set expressions you learn whole: 来得及 / 来不及 'in time / too late', 受得了 / 受不了 'can / can't stand', plus negative-only 了不起 'amazing', 怪不得 'no wonder', 恨不得 'wish one could', 巴不得 'can't wait for'.
- Potential + Resultative: 看得懂 / 看不懂HSK 3 — Any resultative complement flips into a 'can / can't' form just by inserting 得 or 不: 听得懂 / 听不懂 'can / can't understand', 做得完 / 做不完 'can / can't finish', 找得到 / 找不到 'can / can't find' — and the negative test tells this 得 apart from the degree 得.
- Resultative 完: Finishing an ActionHSK 2 — 完 (wán) is the resultative that says an action reached its endpoint or a quantity was used up — 吃完 (finish eating), 做完 (finish doing), 用完 (use up); distinct from 了, negated with 没.
- Potential Complements 可能补语HSK 3 — The potential complement bakes 'can / can't' into the verb–result unit by slipping 得 (de, able) or 不 (bu, unable) into the seam: 看得懂 'can understand' vs 看不懂 'can't understand', 吃得完 vs 吃不完 — inherent possibility, and the negative form does almost all the work.