不
bù
Standard negation with "bu"
不 is the default "not" — it negates habits, states, opinions and the future.
不 + Verb / Adj.
How it works
Put 不 directly in front of the verb or adjective: 我不去, 他不高兴, 这不是我的.
不 covers everything except completed past actions, which take 没 instead. So 我不喝酒 means I don't drink, as a matter of habit, while 我没喝酒 means I didn't drink (this time).
The tone of 不 changes: it is bù normally, but bú before a fourth-tone syllable — 不是 is bú shì.
Examples
tā men bú shì huài hái zi
他们不是坏孩子。
They aren't bad kids.
wǒ bù hē kā fēi
我不喝咖啡。
I don't drink coffee.
míng tiān wǒ bú qù
明天我不去。
I'm not going tomorrow.