必须、必需、必要
must (do) / essential (thing) / necessary (worth doing)
Structure
主语 必须 动词 （一定要做） · 必需 的东西 （少不了） · 有／没有 必要 动词 （值得、需要）
What it means
Three look-alikes: 必须 “must (do)”, 必需 “essential, cannot do without (a thing)”, 必要 “necessary, worth doing”.
How it is built
必须 + verb: 你必须戒烟 (you must quit smoking). 必需 with things: 必需品 (essentials). 有／没有 + 必要 + verb: 没有必要去大医院 (no need to go to a big hospital).
When to use it
An action you must take → 必须; a thing you must have → 必需; whether it is worth doing at all → 必要 (also 必要的检查, 在必要时). 必须 and 必需 sound alike (bìxū), so the mix-up is in writing.
Watch out
✗ 必需戒烟 ✓ 必须戒烟: 必需 never goes before a verb. ✗ 不必须 ✓ 不必 or 不用: that is the negative of 必须.
Examples
要做出准确的诊断，必须先做化验和检查。
To make an accurate diagnosis, lab tests and a scan must be done first.
水和常用药是出远门的必需品。
Water and everyday medicines are essentials for a long journey.
一点儿小感冒，没有必要去大医院排队。
There is no need to queue at a big hospital for a slight cold.
Learn this in Lesson 47 · HSK 5–6: 去医院看病 (Seeing a doctor)
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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