未 and 勿: written negation (has not, do not)
【高23】【高24】副词 / adverbs (否定)
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
未 and 勿 are two written negatives. 未 negates a fact, like 没(有): “has not (yet), did not”. It forms common blocks: 尚未 / 还未 (not yet), 未曾 (never, not once), 未能 (was unable to, did not manage to) and 未经 + noun or verb (without having been…: 未经批准, “without approval”, 未经证实, “unconfirmed”).
勿 forbids or wishes, like 别 or 不要: “do not”. You read it on signs and notices (请勿吸烟), in letters and polished wishes (勿忘). It is never used to state a fact.
In speech you keep 没(有), 别 and 不要. Neither takes 了. And 未 negates what has not happened, not what you intend to do: “I won't go tomorrow” stays 我明天不去.
Examples
请勿吸烟。
Qǐng wù xīyān.No smoking, please.
他至今还未和我联系。
Tā zhìjīn hái wèi hé wǒ liánxì.He still hasn't contacted me.
希望各位勿忘十年后的约定。
Xīwàng gèwèi wù wàng shí nián hòu de yuēdìng.I hope you will all remember our appointment ten years from now.
因天气原因，航班未能按时起飞。
Yīn tiānqì yuányīn, hángbān wèi néng ànshí qǐfēi.Because of the weather, the flight was unable to take off on time.
这位老教授一生未曾离开过这座小城。
Zhè wèi lǎo jiàoshòu yìshēng wèicéng líkāi guo zhè zuò xiǎochéng.This old professor never left this small town in his whole life.
未经本人同意，任何单位不得公开个人信息。
Wèijīng běnrén tóngyì, rènhé dānwèi bùdé gōngkāi gèrén xìnxī.Without the person's consent, no organisation may make personal information public.
Common mistakes
✗ 他未去过了。 → ✓ 他未曾去过。 (no 了 after 未, which negates a fact like 没).
✗ 他勿去。 → ✓ 他不去。 (勿 forbids or wishes, it never states a fact).
✗ 我明天未去。 → ✓ 我明天不去。 (未 negates what has not happened; an intention is negated with 不).