Obligation: 必须, 得 (děi), 不用
能愿动词 / modal verbs
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
Subject + 必须 / 得 + Verb ｜ 不用 / 不必 + Verb
To say "must, have to":
- 必须 (bìxū): strong obligation, a rule, absolute necessity, neutral to formal.
- 得 (děi, mind the pronunciation!): "have to, gotta", very colloquial.
The negative is not 不必须 or 不得: say 不用 (no need to) or, more formally, 不必.
你必须去 → 你不用去 (you don't need to go).
Examples
感冒了，你必须多喝水、多休息。
Gǎnmào le, nǐ bìxū duō hē shuǐ, duō xiūxi.You've got a cold, so you must drink lots of water and rest.
太晚了，我得走了。
Tài wǎn le, wǒ děi zǒu le.It's late, I've got to go.
你不用担心，只是小问题。
Nǐ bú yòng dānxīn, zhǐshì xiǎo wèntí.No need to worry, it's just a minor problem.
Common mistakes
✗ 你不必须来。 → ✓ 你不用来。 / 你不必来。
✗ Reading 得 as dé: when it means "must", 得 is read děi.