不了 vs 不完 (buliǎo vs buwán): potential complements for inability and incompletion
Both 不了 and 不完 are potential complements that express inability, but they differ in focus: 不了 indicates that completing the action is impossible due to capacity or constraints (e.g., too difficult, not allowed), while 不完 emphasizes that finishing is impossible because of an extensive quantity or duration. Choosing the right one depends on whether the barrier is inherent or the amount is overwhelming.
不了 (buliǎo) and 不完 (buwán) are both negative potential complements attached directly to verbs, meaning 'cannot' or 'unable to'. 不了 conveys that the action cannot be completed or even done at all due to a limitation—physical, situational, or inherent—while 不完 specifically stresses that the action cannot be finished because there is too much of something (e.g., quantity, time). For example, 吃不了 can mean 'cannot eat' (allergic or too full) or 'cannot finish eating' (too much), but 吃不完 only means 'cannot finish eating' (too much food). The core mental model: think of 不了 as 'can't manage' (general inability) and 不完 as 'can't reach the end' (incompletion due to extent).
When to use each
Use 不了 after a verb to indicate that the action cannot be completed or even attempted because of a constraint—such as the subject's ability, external rules, or an insurmountable obstacle. Common in expressing 'cannot' for tasks that are too difficult, impossible, or not allowed (e.g., 去不了 'can't go', 做不了 'can't do'). It often implies a categorical inability rather than a mere failure to finish.
不了 can also appear after adjectives to mean 'cannot become' (e.g., 好不了 'can't get better'), and it sometimes overlaps with 不完 when the verb implies a finishable action, but the focus is on the impossibility of the entire action, not just the endpoint.
Use 不完 after a verb to express that the action cannot be completed because there is an excessive quantity of items or a long duration that prevents reaching the end. It focuses on the unfinished state due to an overwhelming amount, not on a fundamental inability to start. For example, 写不完 'can't finish writing' (too many words), 吃不完 'can't finish eating' (too much food).
不完 always implies a telic verb that has a natural endpoint; it is not used for states or actions without a clear finish (e.g., 爱不完 is ungrammatical in standard Chinese).
At a glance
| 不了 | 不完 | |
|---|---|---|
| Core meaning | Inability to complete or perform the action due to a constraint | Inability to finish the action due to quantity or extent |
| Type of barrier | Capacity, feasibility, rule, inherent difficulty | Amount, duration, volume |
| Verb requirement | Works with most action verbs, including atelic ones (e.g., 等不了 'can't wait') | Only with telic verbs that have a clear endpoint (e.g., 做完, 吃完) |
| Example: 吃 | 吃不了: cannot eat (allergic, full) or cannot finish eating (too much, but focus on overall inability) | 吃不完: cannot finish eating because there's too much food |
Examples
- 不了我吃不了辣。Wǒ chībuliǎo là.I can't eat spicy food.不了 expresses inability due to personal tolerance; 不完 would be incorrect here because the issue is not about finishing a quantity.
- 不完这么多菜，我吃不完。Zhème duō cài, wǒ chībuwán.With so many dishes, I can't finish eating them all.不完 focuses on the large amount of food; 吃不了 could also work but would shift the nuance to 'can't manage to eat' (possibly also implying inability to start).
- 不了今天太忙了，我开会去不了。Jīntiān tài máng le, wǒ kāihuì qùbuliǎo.I'm too busy today, I can't go to the meeting.Context makes the action impossible despite desire; 不完 would not fit because 'going' is not a finishable action.
- 不完作业太多了，我写不完。Zuòyè tài duō le, wǒ xiěbuwán.There's too much homework; I can't finish writing it.Quantity of homework prevents completion; 写不了 might suggest the homework is too difficult to write at all.
- 不了他得了重病，好不了了。Tā déle zhòngbìng, hǎobuliǎo le.He's got a serious illness; he can't get better.不了 after an adjective shows impossibility of a change; 不完 is not used with adjectives.
- 不完时间不够，我们看不完这部电影。Shíjiān bú gòu, wǒmen kànbuwán zhè bù diànyǐng.There isn't enough time; we can't finish watching this movie.The shortage of time prevents reaching the end; 看不了 would mean 'can't watch at all' (e.g., no permission).
Common mistakes
- Using 不完 for an inability that is not about quantity: e.g., ✗ 我吃不完美食 (for 'I can't eat gourmet food' — should be 吃不了).
- Using 不了 for a clear quantity issue when you mean 'can't finish': e.g., ✗ 我吃不了那么多饭 (ambiguous; better to use 吃不完 if focusing on the large amount).
- Using 不完 after a verb without a clear endpoint: e.g., ✗ 我等不完他 (for 'I can't wait for him' — should be 等不了).
- Confusing the two in fixed expressions: e.g., 受不了 (cannot bear) uses 不了, never 不完.
FAQ
- When do I use 不了 vs 不完?
- Use 不了 when the action cannot be done at all due to a limitation (e.g., difficulty, permission, capacity). Use 不完 when the action cannot be finished because there is too much of something (quantity, distance, time). Think of 不了 as 'can't' and 不完 as 'can't finish'.
- Can 吃不了 and 吃不完 be used interchangeably?
- Sometimes, but only when the context is about large quantity. For example, 这些菜我吃不了 and 这些菜我吃不完 can both mean 'I can't finish these dishes', but 吃不了 often carries an additional sense of 'I can't eat them (at all)' due to fullness or other constraints. If the barrier is clearly quantity, 吃不完 is more precise.
- Is 不了 always negative? Can I use 得了 for the positive?
- Yes, 不了 is the negative form; the positive potential complement is 得了 (deliǎo), e.g., 吃得了 'can eat / can finish'. For 不完, the positive is 得完 (de wán), e.g., 吃得完 'can finish eating'. Both follow the same pattern of 得/不 + complement.
- Why can't I use 不完 with '去' or '等'?
- Because 去 (go) is a motion verb without a natural endpoint, and 等 (wait) is a durative verb; 不完 requires a telic action that can logically be finished. For such verbs, use 不了 to express inability.