不能 vs 不可以 (bù néng vs bù kěyǐ): saying 'may not'
Both 不能 and 不可以 express prohibition in Chinese, but they differ in strength and nuance. 不可以 is a stronger, more formal prohibition rooted in rules or morality, while 不能 is broader, often indicating practical impossibility or circumstantial constraint. The choice depends on whether the prohibition comes from an explicit rule or from external circumstances.
Both 不能 and 不可以 are negative forms used to deny permission or possibility, but they are not interchangeable in all contexts. 不可以 is a direct negation of 可以, meaning 'not allowed' according to rules, laws, or explicit bans. 不能 is the negation of 能, covering both 'cannot' due to physical inability or circumstance and softer prohibition. The core distinction is that 不可以 is rule-based and stronger, while 不能 is more situational and can also express inability. Learners often overuse 不能 for prohibition when 不可以 would be more precise, or use 不可以 for inability, which is incorrect.
When to use each
Use 不能 to express that something is not possible due to external circumstances, physical constraints, or practical limitations. It can also indicate prohibition, but the prohibition is softer or implied by situation rather than by explicit rule. For example, '你不能在教室里吃东西' can mean 'you can't eat in the classroom' (because it's messy) or 'you're not allowed'.
不能 can also express inability (e.g., physical or situational), but never a lack of learned skill — that uses 不会.
Use 不可以 to express a clear, explicit prohibition based on rules, regulations, laws, or strong moral/social norms. It is more formal and authoritative than 不能. For example, '公共场所不可以吸烟' means 'You must not smoke in public places' (it's illegal or against rules).
不可以 is less common in casual speech than 不能. In everyday prohibition, 不能 is often acceptable, but 不可以 adds emphasis and formality.
At a glance
| 不能 | 不可以 | |
|---|---|---|
| Core meaning | Cannot (inability/prohibition) | Must not (prohibition) |
| Strength of prohibition | Weaker, situational | Stronger, rule-based |
| Can imply physical inability? | Yes | No |
| Common in everyday speech? | Yes, very common | Less common, more formal |
| Affirmative counterpart | 能 (can) | 可以 (may) |
Examples
- 不能这里不能停车。Zhèlǐ bù néng tíng chē.You cannot park here.This could be due to a sign (prohibition) or simply because there's no space (circumstance).
- 不可以考试的时候不可以作弊。Kǎoshì de shíhou bù kěyǐ zuòbì.You are not allowed to cheat during exams.Rule-based prohibition that is strong and explicit.
- 不能他腿受伤了，不能走路。Tā tuǐ shòushāng le, bù néng zǒulù.He injured his leg and cannot walk.Physical inability, not a prohibition.
- 不可以图书馆里不可以大声说话。Túshūguǎn lǐ bù kěyǐ dàshēng shuōhuà.You must not talk loudly in the library.Rule-based prohibition (library rule).
- 不能下雨了，不能出去玩。Xiàyǔ le, bù néng chūqù wán.It's raining, so we can't go out to play.Circumstantial impossibility, not a rule.
- 不能这个房间不能抽烟吗？Zhège fángjiān bù néng chōuyān ma?Can't we smoke in this room?Asking about a likely prohibition or practical constraint; 不可以 would be more formal.
Common mistakes
- Using 不可以 for physical inability (e.g., '他病了，不可以走路' should be 不能).
- Using 不能 for strong rule-based prohibition when 不可以 is more precise (e.g., in official signs, 不可以 is clearer).
- Overusing 不能 for situational prohibition when the context implies an explicit rule; e.g., '图书馆里不能吃东西' is fine but 不可以 is better for library rules.
- Confusing 不能 with 不会 for lack of learned skill (e.g., '我不能游泳' for 'I can't swim' is wrong; use 不会).
FAQ
- When do I use 不能 vs 不可以?
- Use 不能 when the prohibition or impossibility is due to circumstance, physical limits, or soft situational rules. Use 不可以 when the prohibition is based on an explicit rule, law, or moral ban. 不可以 is stronger and more formal.
- Is 不可以 always stronger than 不能?
- Yes, 不可以 typically conveys a stronger, more authoritative prohibition. 不能 can express the same prohibition but with less emphasis, and it is more common in everyday speech for both prohibition and inability.
- Can I use 不能 to mean 'must not'?
- Yes, 不能 can mean 'must not' in many contexts, especially when the prohibition is implied by situation or practical reason. However, if you want to be clear that it's a rule or order, 不可以 is more suitable.
- What is the difference in tone between 不能 and 不可以?
- 不可以 sounds more formal, strict, and rule-based. 不能 is more neutral and versatile; it can sound softer as a prohibition or simply describe impossibility. In written rules (e.g., signs), 不 can also be used alone, but 不可以 is clear and authoritative.