Negation with 没 / 没有

没 (méi) and 没有 (méiyǒu) serve two main purposes in Chinese. First, 没有 is the only way to negate 有 (to have / there is). "I have money" (我有钱) becomes "I don't have money" (我没有钱). You can never say 不有 — it simply does not exist in Chinese.

Second, 没 is used to negate completed actions — things that did not happen in the past. "I didn't eat" is "我没吃" (wǒ méi chī). "She didn't come" is "她没来" (tā méi lái). When you use 没 to negate a past action, you must not add 了 after the verb, because 了 marks completion and 没 denies that the action was completed — the two contradict each other.

The key difference between 不 and 没 comes down to this: 不 is about willingness, habit, and the future ("I don't eat meat" = I choose not to), while 没 is about whether something actually happened or exists ("I didn't eat meat" = the action did not occur). Mixing these up is one of the most common mistakes for beginners, so always ask yourself: am I talking about what happened, or about a general state or choice?