must; have to
HSK level
必须 is written with 14 strokes (必: 5, 须: 9). The animation replays automatically.
必须 (bìxū) is the adverb 'must / have to,' expressing obligation or necessity that comes from rules, logic, or strong personal resolve.
It is placed before the verb: 你必须去 (you must go), 我们必须准时 (we must be on time). Two key differences from English 'must': first, 必须 carries a tone of external requirement or firm necessity — for softer 'should' use 应该 (yīnggāi), and for casual 'gotta' use 得 (děi); second, the negative is NOT 不必须. To say 'don't have to,' use 不必 (bùbì) or 不用 (búyòng); to say 'must not,' use 不能 (bùnéng) or 不可以 (bù kěyǐ).
必须 itself stays in the affirmative. It is common in signs, regulations, and any context where the speaker wants the obligation to sound firm.
Note: Slightly stronger and more formal than 得 (děi). Use 必须 in writing, instructions, rules; use 得 in casual speech.
Character by character
Memory hook: Two 'must' characters in a row — necessity doubled.
明天的会议你必须参加。
Míngtiān de huìyì nǐ bìxū cānjiā.
You must attend tomorrow's meeting.
neutral
学生必须按时交作业。
Xuéshēng bìxū ànshí jiāo zuòyè.
Students must hand in their homework on time.
written
我们必须六点之前到机场。
Wǒmen bìxū liù diǎn zhīqián dào jīchǎng.
We have to get to the airport before six.
neutral
想学好中文，就必须多说多练。
Xiǎng xué hǎo Zhōngwén, jiù bìxū duō shuō duō liàn.
If you want to master Chinese, you have to speak and practice a lot.
neutral
得 is the spoken, casual version: 我得走了 (I gotta go). 必须 is more formal and emphatic: 我必须走 (I must leave). In conversation 得 is far more common; 必须 sounds slightly heavier.
必要 is an adjective/noun meaning 'necessary / necessity' — 没有必要 (there's no need). 必须 is the adverb 'must' that goes before a verb. Don't say 必要去 — say 必须去 or 有必要去.
必然 means 'inevitable / inevitably' — about logical certainty, not obligation. 必然结果 (inevitable result) is different from 必须做 (must do).
不必 is the negation pair — 'don't have to / no need to.' Beginners often write 不必须, which is wrong. 必须 has no direct negative; use 不必 or 不用
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