可以 kěyǐ
可以（kěyǐ）means “can / may: permission or possibility”. 可以 before a verb means either permission ('may I…. Formation: 可以 + 动词（否定：不可以/不能）
can / may: permission or possibility
HSK2Formation
可以 + 动词（否定：不可以/不能）
Explanation
可以 before a verb means either permission ('may I…?') or that something is feasible/allowed. To ask permission, add 吗: 可以进来吗? The common negative is 不可以 ('may not') or 不能.
Examples
我 可以 进来吗？
wǒ kěyǐ jìn lai ma?
May I come in?
这个水 可以 喝。
zhège shuǐ kěyǐ hē.
This water is safe to drink.
Note
In speech the negative is usually 不能 rather than 不可以. 可以 alone can answer 'OK'.
FAQ
可以 — what does it mean and how is it used?
can / may: permission or possibility. 可以 before a verb means either permission ('may I…?') or that something is feasible/allowed. To ask permission, add 吗: 可以进来吗? The common negative is 不可以 ('may not') or 不能.
可以 — how do you form it?
可以 + 动词（否定：不可以/不能）
可以 — any usage notes?
In speech the negative is usually 不能 rather than 不可以. 可以 alone can answer 'OK'.