比较since和for
Since 用来说明动作起始时间，for用来说明动作延续时间长度。 I have lived here for more than twenty years. I have lived here since I was born..
My aunt has worked in a clinic since 1949.
Some new oilfields have been opened up since 1976. I have known Xiao Li since she was a little girl.
My brother has been in the Youth League for two years. I have not heard from my uncle for a long time. 注意：并非有for 作为时间状语的句子都用现在完成时。 I worked here for more than twenty years. (我现在已不在这里工作。)
I have worked here for many years. (现在我仍在这里工作。)
小窍门：当现在完成时+一段时间，这一结构中，我们用下面的公式转化，很容易就能排除非延续动词在完成时中的误使。
1)(对) Tom has studied Russian for three years.
= Tom began to study Russian three years ago, and is still studying it now.
2)(错) Harry has got married for six years.
= Harry began to get married six years ago, and is still getting married now.
显然，第二句不对，它应改为 Harry got married six years ago.或 Harry has been married for six years.
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、1980, last month, half past six)。
I have been here since 1989. 2) since +一段时间+ ago
I have been here since five months ago. 3) since +从句
Great changes have taken place since you left.
Considerable time has elapsed since we have been here. 4) It is +一段时间+ since从句
It is two years since I became a postgraduate student.
延续动词与瞬间动词
1) 用于完成时的区别
延续动词表示经验、经历； 瞬间动词表示行为的结 果，不能与表示段的时间状语连用。
He has completed the work.他已完成了那项工作。 (表结果) I've known him since then. 我从那时起就认识他了。(表经历) 2)用于till / until从句的差异
延续动词用于肯定句，表示\做……直到……\\到……，才……\
He didn't come back until ten o'clock. 他到10 点才回来。
He slept until ten o'clock. 他一直睡到10点。 典型例题
1. You don't need to describe her. I ___ her several times. A. had metB. have metC. metD. meet
答案B. 首先本题后句强调对现在的影响，我知道她的模样，你不用描述。再次，several times告知为反复发生的动作，因此用现在完成时。
'm sorry to keep you waiting.
---Oh, not at all. I ___ here only a few minutes. A. have beenB. had beenC. wasD. will be
答案A. 等待的动作由过去开始，持续到现在，应用现在完成时。
过去完成时
1） 概念：表示过去的过去
----|-----------|-----------|---->其构成是had +过去分词构成。 那时以前那时现在 2） 用法
a.在told, said, knew, heard, thought等动词后的宾语从句。 She said (that) she had never been to Paris. b. 状语从句
在过去不同时间发生的两个动作中，发生在先，用过去完成时；发生在后，用一般过去时。
When the police arrived, the thieves had run away.
c. 表示意向的动词，如hope, wish, expect, think, intend, mean, suppose等，用过去完成时表示\原本…，未能…\
We had hoped that you would come, but you didn't.
3)过去完成时的时间状语before, by, until , when, after, once, as soon as。 He said that he had learned some English before.
By the time he was twelve, Edison had began to make a living by himself. Tom was disappointed that most of the guests had left when he arrived at the party.
典型例题
The students ___ busily when Miss Brown went to get a book she ___ in the office.
A. had written, leftB，were writing, has leftC. had written, had leftD. were writing, had left
答案D. \把书忘在办公室\发生在\去取书\这一过去的动作之前，因此\忘了书\这一动作发生在过去的过去，用过去完成时。句中when表示的是时间的一点，表示在\同学们正忙于……\when所引导的动作发生。因此
前一句应用过去进行时。
注意：had no … when还没等…… 就…… had no sooner… than刚…… 就……
He had no sooner bought the car than he sold it.
用一般过去时代替完成时
1)两个动作如按顺序发生，又不强调先后，或用then，and，but 等连词时，多用一般过去时。
When she saw the mouse，she screamed. My aunt gave me a hat and I lost it.
2 ) 两个动作相继发生，可用一般过去时；如第一个动作需要若干时间完成，用过去完成时。
When I heard the news, I was very excited.
3)叙述历史事实，可不用过去完成时，而只用一般过去时。
Our teacher told us that Columbus discovered America in 1492.
将来完成时
1) 构成will / be going to do sth. 2) 概念
a. 状态完成：表示某事继续到将来某一时为止一直有的状态。
b. 动作完成：表示将来某一时或另一个将来的动作之前，已经完成的动作或一获得的经验。
They will have been married for 20 years by then.
You will have reached Shanghai by this time tomorrow.
现在进行时
现在进行时的基本用法：
a. 表示现在( 指说话人说话时) 正在发生的事情。 We are waiting for you.
b. 习惯进行：表示长期的或重复性的动作，说话时动作未必正在进行。 Mr. Green is writing another novel. (说话时并未在写，只处于写作的状态。) She is learning piano under Mr. Smith.
c. 表示渐变的动词有：get, grow, become, turn, run, go, begin等。 The leaves are turning red. It's getting warmer and warmer.
d. 与always, constantly, forever 等词连用，表示反复发生的动作或持续存在的状态，往往带有说话人的主观色彩。
You are always changing your mind. 典型例题
My dictionary ___, I have looked for it everywhere but still___ it. A. has lost, don't find B. is missing, don't findC. has lost, haven't foundD. is missing, haven't found.
答案D. 前句是一个仍在持续的状态，应用进行时，由于没有找到，其影响仍然存在，应用完成时，瞬间动词用于否定式时可用于完成时。
不用进行时的动词
1) 事实状态的动词
have, belong, possess, cost, owe, exist, include, contain, matter, weigh, measure, continue
I have two brothers.
This house belongs to my sister. 2) 心理状态的动词
Know, realize, think see, believe, suppose, imagine, agree, recognize, remember, want, need, forget, prefer, mean, understand, love, hate
I need your help.
He loves her very much. 3 ) 瞬间动词
accept, receive, complete, finish, give, allow, decide, refuse. I accept your advice. 4) 系动词
seem, remain, lie, see, hear, smell, feel, taste, get, become, turn You seem a little tired.
过去进行时
1） 概念：表示过去某时正在进行的状态或动作。
2） 过去进行时的主要用法是描述一件事发生的背景；一个长动作发生的时候，另一个短动作发生。
3) 常用的时间状语
this morning, the whole morning, all day yesterday, from nine to ten last evening, when, while
My brother fell while he was riding his bicycle and hurt himself. It was raining when they left the station.
When I got to the top of the mountain, the sun was shining. 典型例题
1) Mary ___ a dress when she cut her finger. A. madeB. is makingC. was makingD. makes
答案C. 割伤手指是已发生的事情，应用过去时。同时，when表时间的同时性，\玛丽在做衣服时\提供事情发生的背景，因此用过去进行时。
2) As she ___ the newspaper, Granny ___ asleep. read； was fallingB. was reading； fellC. was reading； was fallingD. read；fell
答案B.句中的as = when, while，意为\当……之时\。描述一件事发生的背景时，用过去进行；一个长动作发生的时候，另一个短动作发生。句意为 \在她看报纸时，奶奶睡着了。\句中的 fell (fall的过去时)，是系动词，后跟形容词，如：fall sick。
将来进行时
1) 概念：表示将来某时进行的状态或动作，或按预测将来会发生的事情。