The negative particles 未 and 勿
We use both 未 and 勿 to make a negation. However their usage is slightly different.
The negative particle 未
We use the negative particle 未 
to express the current state of a situation. It is usually stated before a verb and forms an adjective with it.
to express the current state of a situation. It is usually stated before a verb and forms an adjective with it.Examples
他们衣服肮脏，头发未洗
Their clothes are dirty and their hair is unwashed
tāmen yīfu āngzang, tóufa wèi xǐ
未使用元素
unused elements
wèi shǐyòng yuánsù
Pay attention
Sometimes 未 is used as part of terms. For example:
未成年
未婚
未婚 When we use it in the past tense, it has the meaning “not yet”. It is often used alongside 从 or 从来 “never before”.
or 从来 “never before”.Examples
我以前从未见过他
I've never seen him before
wǒ yǐqián cóng wèi jiànguò tā
他至今还未和我联系
He hasn't contacted me yet
tā zhìjīn hái wèi hé wǒ liánxì
The negative particle 勿
We use the negative particle 勿 to express that an action should not be done. We should state it before a predicate which is expressed by a verb.
to express that an action should not be done. We should state it before a predicate which is expressed by a verb.Examples
请勿进入
Please do not enter
qǐng wù jìnrù
勿为他人成功而牺牲生活
Don't sacrifice your life for the success of others
wù wèi tārén chénggōng ér xīshēng shēnghuó
Pay attention
The negative particle 勿 is often used on the prohibitive signs.
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