Difference between 别 and 不 I know that a typical way to negate a verb is to stick 不 in front of it. But I learned some phrases that use 别 instead: 别担心, 别客气 and so on, all of them in short polite fixed phrases. I know that I could change 别 into 不 in those phrases too.

So what's the difference between those words?
不 means "not" and 别 means "do not." One is a simple negation, and the other is a (negative) command.