‘Méi 没’ and ‘bù 不’ are both negation words in Mandarin Chinese, but we use them in different ways. To use them correctly is notoriously difficult for many Chinese language learners.
Using ‘bù 不’
First, to indicate that an action does not happen now or will not happen in the future, use the negation word ‘bù 不’. For example, “I don’t eat breakfast” (我不吃早饭 Wǒ bù chīzǎofàn). “I don’t want to eat breakfast tomorrow” (我明天不想吃早饭 Wǒ míngtiān bùxiǎng chīzǎofàn).
Second, to indicate that an action did not happen in the past. In this situation, you should use the negation word ‘méi 没’ or ‘méi yǒu 没有’. For example, “I didn’t eat breakfast” (我没吃早饭 Wǒ méi chīzǎofàn).
‘Méi 没’ and ‘bù 不’ don’t mean the same thing
You may think ‘bù 不’ and ‘méi 没’ mean the same thing but they don’t. Let’s compare these two sentences:
“我不吃早饭 Wǒ bù chīzǎofàn” means I don’t eat breakfast. When you use ‘bù 不’ to negate a verb, it means the action doesn’t happen or will not happen. This sentence implies that I don’t have the habit of eating breakfast. I just don’t do that.
But “我没吃早饭 Wǒ méi chīzǎofàn” means I didn’t eat breakfast yet. Maybe I forgot to eat breakfast or maybe I didn’t have time to eat breakfast, the result is that I didn’t have breakfast.