Prohibited = 禁止 Smoking Prohibited = 禁止 吸烟, less formal 不許, 不允, 不準 cannot = 不可 Unable = 不能

Like Clarence said, 能 and 可以 are interchangable in some context. 可以 used as prohibiton: (1) 你不可以在这儿抽烟。(You’re not allowed to smoke here) (2) 不可以随地吐痰。(No spitting) You can also use 能 in the sentence #1, 你不能在这儿抽烟 (you can't smoke here) * Notice that the tone between the sentence 可以 and 能 are slightly different. 可以 sounds more strict. 可以 can also means 能/能够, for example: (1) 等我拿了奖金，我就可以把这辆车买下来。(Wait till I get the scholarship, I would be able to buy this car) (2) 你不可以这样做，这是犯法的。(You couldn’t do this, it’s against the law) Compare these sentences: (1) a. 你能不能帮我个忙？(Can you help me?) b. 你可不可以帮我个忙？(Can you help me?) - 可以。(Yes, I can) - 对不起，我不能 （不行/不可以）。因为我现在很忙。(I’m sorry, I can’t. I’m busy right now) Hope they help, Terecia

不能 = unable to do 不可以 = not allowed to do Sometimes these two words can replace each other, but usually just like this.