Personal and factual statements
A slightly less intuitive but more encompassing explanation is that 不 is used to negate statements which are based on personal circumstances, whereas 没 is used to negate statements of fact.
- 我 没 去 (I didn't go – an objective statement not reliant on personal circumstances)
- 我 不 去 (I won't go – a decision based on personal circumstances. I won’t go because I don't have the money, because I'm busy or so on. This decision is up to me)
- 我 今天没 吃饭 (I haven't eaten today. This is a factual statement)
- 我 今天不 吃饭 (I'm not eating today. This is an opinion based on personal reasons; perhaps the speaker is feeling ill, is too busy or is too lazy. Again, this is my decision)
With this clear, it is now easier to explain another two uses of 不 and 没。
Second, statements with negating adjectives are generally personal statements, therefore we do not use 没 to negate adjectives. We can only say "不好" or "不漂亮", not "没好" or "没漂亮".
The examples below are a little more difficult, as these statement are very similar. However the same rule applies:
- 水 没 凉 (the water hasn't cooled down yet – this emphasizes that the objective process of water cooling hasn't finished yet, as it hasn't yet reached room temperature)
- 水不 凉 (the water isn't cool – here the speaker is making statement based on their belief of what cool is. I might think this water is cool, but you may not, the standard we use is subjective)
- 我 不 是 这个 意思 (No, you've got me wrong, you've judged the situation wrongly - a personal judgement on my behalf that the listener has misjudged me)
- 我 没有 这个 意思 (I never implied that - an objective fact)