since的四種用法
1) since +過去一個(gè)時(shí)間點(diǎn) (如具體的年、月、日期、鐘點(diǎn)、1980,last month,half past six).
I have been here since 1989.
2) since +一段時(shí)間+ ago
I have been here since five months ago.
3) since +從句
Great changes have taken place since you left.
Considerable time has elapsed since we have been here.
4) It is +一段時(shí)間+ since從句
It is two years since I became a postgraduate student
5.延續(xù)動(dòng)詞與瞬間動(dòng)詞
1) 用于完成時(shí)的區(qū)別
延續(xù)動(dòng)詞表示經(jīng)驗(yàn)、經(jīng)歷； 瞬間動(dòng)詞表示行為的結(jié) 果,不能與表示段的時(shí)間狀語連用.
He has completed the work.他已完成了那項(xiàng)工作.(表結(jié)果)
I've known him since then.我從那時(shí)起就認(rèn)識(shí)他了.(表經(jīng)歷)
since作連詞引導(dǎo)時(shí)間狀語從句的用法.
一、若since引導(dǎo)的狀語從句的謂語動(dòng)詞是終止性的過去時(shí),則從句表示的時(shí)間是“從動(dòng)作開始的那一時(shí)刻起”.如：
He has studied very hard since he came to our school.自從他來到我們學(xué)校,他學(xué)習(xí)就非常努力.
We have been missing them since they left here自從他們離開這里,我們就一直很想念他們.
這是最常見的一種用法,此處不再多述.
二、若since引導(dǎo)的狀語從句的謂語動(dòng)詞是持續(xù)性動(dòng)詞或表示狀態(tài)的動(dòng)詞的過去時(shí)時(shí),則從句表示的時(shí)間是“從那持續(xù)動(dòng)作或狀態(tài)結(jié)束時(shí)算起”.如：
I haven’t heard any noise since I slept.Sleep 為持續(xù)性動(dòng)詞,sleep的動(dòng)作結(jié)束時(shí),即“醒來”時(shí),這句應(yīng)譯為“我醒后還未聽到任何聲音”.
John is now with his parents in New York,it is already three years since he was a teacher約翰現(xiàn)在和父母一起住在紐約,他不當(dāng)教師已經(jīng)三年了.
本文開始出現(xiàn)的那個(gè)句子就可以譯為“自從我離開上海,就再也沒有收到他的信.”這種譯法常被人們誤用,我們不妨再多舉幾個(gè)例子看看：
How long is it since you lived in Shanghai?你離開（沒住在）上海多久了?
It is half a month since he was a League member.他退團(tuán)（不當(dāng)團(tuán)員）半個(gè)月了.
It’s been quite some time since I was last in London我離開倫敦已很長(zhǎng)時(shí)間了.
比較：He has written to me frequently since I was ill.自從我病愈以來,他屢次給我寫信.（從句謂語為狀態(tài)動(dòng)詞）
He has written to me frequently since I fell ill.自從我生病以來,他就屢次給我寫信.（從句謂語為終止性動(dòng)詞）
三、若since引導(dǎo)的狀語從句的謂語為持續(xù)性動(dòng)詞的現(xiàn)在完成時(shí),則表示動(dòng)作和狀態(tài)延續(xù)到現(xiàn)在（說話時(shí)刻）,其表示的時(shí)間的起點(diǎn)應(yīng)從動(dòng)作發(fā)生之時(shí)算起.如：
I haven’t heard from him since he has lived there.
這里has lived表示動(dòng)作的持續(xù)性,時(shí)間的起點(diǎn)應(yīng)從：“開始居住”時(shí)算起.因此此句可理解為“自從他（開始）住在那兒起,我就一直沒收到他的來信”.
Since we have owned a car,we have gone camping every year.自從我們自己有了汽車,我們每年都去野營.
試比較：1.Since I’ve been at this school,we have had three headmasters.自從我到這所學(xué)校,我們已換了三個(gè)校長(zhǎng)了.
Since I was at this school,they have had three headmasters.自從我離開這所學(xué)校,他們已換了三個(gè)校長(zhǎng)了.
2.He has never been to see me since I have been ill.自從我生病以來,他從未來看過我.
He has never been to see me since I was ill.自從我病愈以來,他從未來看過我.
由此可見,since引導(dǎo)的從句持續(xù)動(dòng)詞的一般過去時(shí)和現(xiàn)在完成時(shí)所表示的意思恰好相反.換言之,前者以肯定的語法形式反映著否定的邏輯內(nèi)容,而后者的形式與內(nèi)容是一致的.