since和for用法

since和for用法
since和for用法

since和for用法
since+时间点
for+时间段
Since 用来说明动作起始时间,for用来说明动作延续时间长度.
since的用法主要有两点：一是表示“自从……以来”,二是表示“既然”之意.但如果只了解词的含义,而不了解其用法,在使用时就会造成错误.例如：I have not heard from him since I lived in Shanghai.
不少人会望文生义,将该句译为：“自从我住在上海以来,就再也没有收到他的信了.”而实际上这个句子的译文并非如此,那么正确的含义是什么呢?
下面谈谈since作连词引导时间状语从句的用法.
一、若since引导的状语从句的谓语动词是终止性的过去时,则从句表示的时间是“从动作开始的那一时刻起”.如：
He has studied very hard since he came to our school.自从他来到我们学校,他学习就非常努力.
We have been missing them since they left here自从他们离开这里,我们就一直很想念他们.
这是最常见的一种用法,此处不再多述.
二、若since引导的状语从句的谓语动词是持续性动词或表示状态的动词的过去时时,则从句表示的时间是“从那持续动作或状态结束时算起”.如：
I haven’t heard any noise since I slept. Sleep 为持续性动词,sleep的动作结束时,即“醒来”时,这句应译为“我醒后还未听到任何声音”.
John is now with his parents in New York, it is already three years since he was a teacher约翰现在和父母一起住在纽约,他不当教师已经三年了.
本文开始出现的那个句子就可以译为“自从我离开上海,就再也没有收到他的信.”这种译法常被人们误用,我们不妨再多举几个例子看看：
How long is it since you lived in Shanghai?你离开（没住在）上海多久了?
It is half a month since he was a League member.他退团（不当团员）半个月了.
It’s been quite some time since I was last in London我离开伦敦已很长时间了.
比较：He has written to me frequently since I was ill.自从我病愈以来,他屡次给我写信.（从句谓语为状态动词）
He has written to me frequently since I fell ill.自从我生病以来,他就屡次给我写信.（从句谓语为终止性动词）
三、若since引导的状语从句的谓语为持续性动词的现在完成时,则表示动作和状态延续到现在（说话时刻）,其表示的时间的起点应从动作发生之时算起.如：
I haven’t heard from him since he has lived there.
这里has lived表示动作的持续性,时间的起点应从：“开始居住”时算起.因此此句可理解为“自从他（开始）住在那儿起,我就一直没收到他的来信”.
Since we have owned a car, we have gone camping every year.自从我们自己有了汽车,我们每年都去野营.
试比较：1. Since I’ve been at this school, we have had three headmasters.自从我到这所学校,我们已换了三个校长了.
Since I was at this school, they have had three headmasters.自从我离开这所学校,他们已换了三个校长了.
2.He has never been to see me since I have been ill. 自从我生病以来,他从未来看过我.
He has never been to see me since I was ill. 自从我病愈以来,他从未来看过我.
由此可见,since引导的从句持续动词的一般过去时和现在完成时所表示的意思恰好相反.换言之,前者以肯定的语法形式反映着否定的逻辑内容,而后者的形式与内容是一致的.
至于It is +一段时间+since…的句型与It has been +一段时间+since…意思相同.前者是规范说法,后者是口语说法.
应注意的是,在这种结构中,since引导的从句绝对不能用否定式的谓语动词来表示否定意义,下面两句都错了：
It is a long time since he didn’t study English.
It’s two months since you didn’t come to see me.
正确的说法为：
It’s a long time since he studied English 他好久没学英语了.
You haven’t come to see me for two months. 你有两个月没来看我了.
一、延续性动词和终止性动词的概念
英语中,动词按其动作发生的方式、动作发生过程的长短,可分为延续性动词和终止性动词.
延续性动词表示能够延续的动作,这种动作可以延续下去或产生持久影响.如：learn, work, stand, lie, know, walk, keep, have, wait, watch, sing, read, sleep, live, stay等.
终止性动词也称非延续性动词、瞬间动词或短暂性动词,表示不能延续的动作,这种动作发生后立即结束.如open, close, finish, begin, come, go, arrive, reach, get to, leave, move, borrow,buy等.
二、延续性动词的用法特征
1.延续性动词可以用于现在完成时,其完成时态可与表示"段时间"的状语连用.表示"段时间"的短语有：for two years, during the past three years, since last year, how long等.如：I have learned English since I came here.自从我来到这儿就学英语了.
2.延续性动词不能与表示短暂时间的"点时间"状语连用.如：It raind at eight yesterday morning.(误) rain为延续性动词,而at eight表示"点时间",前后显然矛盾.如果用延续性动词表示一瞬间的动作,可以借助come, begin, get等终止性动词来表示.上句可改为：It began to rain at eight yesterday morning.(正)又如：
-When did you get to know Jack?
-Two years ago.
-Then you've known each other for more than two years.
-That's right.
三、终止性动词的用法特征
1.终止性动词可用来表示某一动作完成,因此可用于现在完成时.如：
The train has arrived.火车到了.
Have you joined the computer group?你加入电脑小组了吗?
2.终止性动词表示的动作极其短暂,不能持续.因此,不可与表示一段时间的状语连用(只限肯定式).如：
(1)他死了三年了.
误：He has died for three years.
正：He has been dead for three years.
正：He died three years ago.
正：It is three years since he died.
正：Three years has passed since he died.
(2)他来这儿五天了.
误：He has come here for five days.
正：He has been here for five days.
正：He came here five days ago.
正：It is five days since he came here.
正：Five days has passed since he came here.
(1)、(2)句中的die、come为终止性动词,不能与表示"段时间"的状语连用.那么,应如何正确表达呢?可以采用下面的四种方法：
(1)将句中终止性动词转换为相应的延续性动词,如上面两例中的第一种正确表达方式.下面列举几例：leave→be away, borrow→keep, buy→have, begin/start→be on, die→be dead, move to→live in, finish→be over, join→be in/be a member of, open sth.→keep sth. open, fall ill→be ill, get up→be up, catch a cold→have a cold.
(2)将句中表示"段时间"的状语改为表示过去确定时间的状语,如下面两例中的第二种正确表达方式.
(3)用句型"It is+段时间+since..."表达原意,如上面两例中的第三种正确表达方式.
(4)用句型"时间+has passed+since..."表达原意,如上面两例中的第四种正确表达方式.
3.终止性动词可用于现在完成时否定式中,成为可以延续的状态,因而可与表示一段时间的状语连用.如：
He hasn't left here since 1986.
I haven't heard from my father for two weeks.
4.终止性动词的否定式与until/till连用,构成"not+终止性动词+until/till ..."的句型,意为"直到……才……".如：
You can't leave here until I arrive.直到我到了,你才能离开这里.
I will not go to bed until I finish drawing the picture tonight.今天晚上直到我画完画,我才上床睡觉.
5.终止性动词可以用于when引导的时间状语从句中,但不可以用于while引导的时间状语从句中.when表示的时间是"点时间"(从句谓语动词用终止性动词),也可以是"段时间"(从句谓语动词用延续性动词).而while表示的是一个较长的时间或过程,从句谓语动词用延续性动词.如：
When we reached London, it was twelve o'clock. (reach为终止性动词)
Please look after my daughter while/when we are away. (be away为延续性动词短语)
6.终止性动词完成时不可与how long连用(只限于肯定式).如：
误：How long have you come here?
正：How long have you been here?
正：When did you come here?

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