Question

完成时中for和since的区别和用法

Answer 1

现在完成时中since和for的区分

Answer 2

since 和 for 的用法及区别：

一、since 的四种用法
1. since + 过去一个时间点（如具体的年、月、日期、钟点、ago. 1990 , last month , half past six
I have been here since 1990. 1990起，我一直在这儿。

2. since+ 一段时间+ago
I have been here since five months ago。自从五个月前，我已经在这儿了。

3. since+从句
Changes have taken place since you left. 自从你走后，已经发生了很大的变化。

4. It is +一段时间+since从句
It is two years since I became an English teacher. 我成为英语老师有两年了。

二、since 和for区别
1. Since +时间点，具体时间
“自从、、、、以来，从、、、以后” 用来说明动作起始时间
I have been in Beijing since 2010.

2. For + 时间段，用来说明动作延续时间长度，因此句中的谓语动词，也应该是延续性动词。
I have been in Beijing for one year。
We have learnt English for about three years.

I have been here for 3 days. (对)
I have arrived here for 3 days.（误）

三、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。

四、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
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。如果用延续性动词性动词来表示一瞬间的动作，可借助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.

五、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.

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

Answer 3

since 和 for 都可以用在现在完成时的句子里，表示“多久（how long）”。
since 用在表示从过去某个时刻到现在，如
since six o’clock（从六点钟起），since last year（从去年开始），since I went away（自从我离开起）等；
for用在表示一直延续到现在的一段时间前，如
for six hours（有六小时了），for tow years（有两年了），for a long time（有好久了）等。
例：
We have studied English for six years.（我们学英语有六年了。）
We have studied English since 2000.（我们从2000年起就学习英语了。）

Answer 4

for后面跟一段时间，since后面跟过去的时间点。