一定 · 必须 · 不一定 · 不用
一定: surely; be sure to · 必须: must, have to
Structure
一定 （+ 要） + 动词 · 必须 + 动词 · 否定： 不一定 · 不用
What it means
一定 means “be sure to” (with 要) or “surely, must be” when you guess. 必须 means “must, have to”, for a rule or a real need.
How it is built
一定要 + verb: 你一定要来！ 一定 + adjective for a guess: 他一定很累. 必须 + verb: 出国必须带护照 (You have to take your passport to go abroad).
When to use it
一定 is a strong wish or a sure guess; 必须 is a rule or need. The negatives differ: 不一定 is “not necessarily” (他不一定来 “he may not come”); “don’t have to” is 不用 (h1-20).
Watch out
✗ 你不必须来。 ✓ 你不用来。 Never say 不必须. And 不一定 means “may not”, not “must not”.
Examples
明天你一定要来！
You must come tomorrow!
出国必须带护照。
You have to take your passport to go abroad.
他明天不一定来。
He may not come tomorrow.
坐地铁不用带护照。
You don’t need your passport for the metro.
Learn this in HSK 2 · Lesson 17: 找工作 (Looking for work)
A dialogue, a reading, word cards with audio and a drill that uses it, in Learn Chinese with Bao. The first lessons of every level are free.
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