古時候,晉獻(xiàn)公想要裁減自己的實力和地盤,就找借口說鄰近的虢(guó)國經(jīng)常侵犯晉國的邊境,要派兵滅了虢國。可是在晉國跟虢國之間隔著一個虞國,討伐虢國必須經(jīng)過虞地。“怎么才能順利通過虞國呢?”晉獻(xiàn)公問手下的大臣。大夫荀息說:“虞國國君是個目光短淺、貪圖小利的人,只有咱們送他價值連城的美玉跟寶馬,他不會不允許借道的。”晉獻(xiàn)公一聽有點舍不得,荀息看出了晉獻(xiàn)公的心思,就說:“虞虢兩國是唇齒相依的近鄰,虢國滅了,虞國也不能獨存,你的美玉寶馬不過是暫時存放在虞公那里罷了。”晉獻(xiàn)公采取了荀息的計策。

　　虞國國君見到這兩們寶貴的禮物,頓時樂不可支,聽到荀息說要借道虞國之事時,當(dāng)時就滿口容許下來。虞國大夫?qū)m之奇據(jù)說后,趕快制止道:“不行,不行,虞國和虢國事唇齒相依的近鄰,咱們兩個小國彼此依存,有事可能自彼幫助,萬一虢國滅了,我們虞國也就難保了。俗話說:‘唇亡齒寒’,不嘴唇,牙齒也保不住啊!借道給晉國萬萬使不得。”虞公說:“人家晉國是大國,當(dāng)初順便送來美玉寶馬和咱們交朋友,難道咱們借條道路讓他們走走都不行嗎?”宮之奇連聲嘆氣,知道虞國離滅亡的日子不遠(yuǎn)了,于是就帶著一家老小離開了虞國。

　　果然,晉國軍隊借道虞國,覆滅了虢國,隨后又把親自迎接晉軍的虞公抓住,滅了虞國。 故事出自《左傳·僖公五年》。成語“唇亡齒寒”,比喻雙方關(guān)系密切,相互依存。

　　During the Spring and Autumn Period (707 - 476 B.C.), Duke Xian of the State of Jin Wanted to expand his position of strength and sphere of influence. Therefore he would like to send his troops to destroy the State of Guo on the pretest that the State of Guo often encroached on theborders of the State of Jin. But there was a third state, the State of Yu,between the State of Jin and the State of Guo, and the Jin army had to cross the State of Yu before it could reach the State of Guo . "How can my army cross the State of Yu without a hitch?" Duke Xian of the State of Jin asked his ministers.Xun Xi , one of the ministers, said, "The monarch of the State of Yu is short - sighted and covets small advantages. If we give him priceless precious stones and fine horses, it is not unlikely that he will allow our army to pass through his country. " Seeing that Duke Xian of the State of Jin was a little bit grudging, Xun Xi continued to say, "The State of Yu and the State of Guo are neighbor stated as closely related as lips and teeth. The State of Yu cannot exist independently if the state of Guo is destroyed. Your precious stones and fime hores are just left in the care of the monarch of the State of Yu." So Duke Xian of the State of Jin accepted Xun Xi's plan. When the monarch of Yu saw the precious gifts, he was elated,and readily promised to let the Jin army pass through his state. Hearing the news, Gong Zhiqi, one of the ministers as the State of Yu, hastened to admonish the monarch, saying," That won't do.For the State of Yu and the State of Guo are neighbor states as closely related as lips and teeth. Our two small states are interdependent, and can help cach other when problems crop up .If the State of Guo were destroyed, it would be difficult for our State of Yu to continue to exist. As the common saying goes, if the lips are gone ,the teeth will be cold, The teeth can hardly be kept if the lips are gone. So it won't do at all to allow the Jin army pass our state." The monarch of the State of Yu said," The State of Jin is a big state. Now they here specially to present gifts to us with the intention of being on friendly terms with us. Under suchcircumstances, how can we refuse to allow them to pass through our state?" Hearing this, Gong Zhiqi sighed repeatedly. Knowing that the State of Yu would soon be destroyed, Gong Zhiqi left the State of Yu together with his whole family.

　　As expected, the troops of the State of Jin, allowed to pass through the State of Yu, destroyed the State of Guo and on their return trip captured the monarch of the State of Yu who went out personally to meet them, thus destroying the State of Yu as Well.

　　This story appears in the chapter " The Fifth Year of Duke Xi " in Zuo zhuan,the famous commentary by Zuo Qiuming on The Spring and Autumn Annals. The set phrase " if the lips are gone, the teeth will be cold " is used to mean that two persons or things share a common lot and that is one fails ,the other is in danger.