現(xiàn)在完成時 和過去完成

定義現(xiàn)在完成時用來表示之前已發(fā)生或完成的動作或狀態(tài)，其結果的確和現(xiàn)在有聯(lián)系。動作或狀態(tài)發(fā)生在過去　但它的影響現(xiàn)在還存在;也可表示持續(xù)到現(xiàn)在的動作或狀態(tài)。其構成：have (has) +過去分詞。

用法：

1)現(xiàn)在完成時所表示的動作在說話之前已完成，但對現(xiàn)在有影響，句中沒有具體的時間狀語。此時多于never， ever， just，before，already，yet等連用。

2)現(xiàn)在完成時所表示的動作開始于過去，持續(xù)到現(xiàn)在，也許還會繼續(xù)持續(xù)下去。常與for，since等一段時間狀語連用。

注意：表示暫短動作的詞(如come，go，borrow，lend，die，bur，marry等)的完成時不能與for，since等表示一段時間的狀語連用。

例如：How long may I keep the book?這本書我可以借多久?

Two weeks

Borrow和lend 都是暫短性動詞，當表示借多久時，用動詞keep

常見的短暫性動詞轉換成延續(xù)性動詞

leave --- be away, borrow --- keep, buy --- have,

begin/start --- be on, die --- be dead, finish --- be over,

join --- be in+組織機構,be a member of+組織機構,

open sth --- keep sth open, fall ill --- be ill,

get up---be up, catch a cold --- have a cold,

come here --- be here, go there --- be there, become --- be,

come back --- be back, fall asleep --- be asleep,

get to/ arrive/reach --- be (in), leave --- be away from,

get to know --- know, go (get) out →be out，

put on→ wear;catch a cold →have a cold等。

例:The old man died 4 years ago.

----The old man has been dead for 4 years.

---- It is 4 years since the old man died.

----Four years has passed since the old man died.

He joined the Party 2 years ago.

-----He has been in the Party for 2 years.

I bought the book 5 days ago.

---- I have had the book for 5 days.

比較過去時與現(xiàn)在完成時

1)過去時表示過去某時發(fā)生的動作或單純敘述過去的事情，強調動作;現(xiàn)在完成時為過去發(fā)生的，強調過去的事情對現(xiàn)在的影響，強調的是影響。

2)過去時常與具體的時間狀語連用，而現(xiàn)在完成時通常與模糊的時間狀語連用，或無時間狀語。

一般過去時的時間狀語:

yesterday, last week，…ago, in1980, in October, just now, 具體的時間狀語

現(xiàn)在完成時的時間狀語

for, since, so far, ever, never, just, yet,　till / until, up to now, in past years, always,

3)現(xiàn)在完成時可表示持續(xù)到現(xiàn)在的動作或狀態(tài)，動詞一般是延續(xù)性的，如live, teach, learn, work, study, know.

過去時常用的非持續(xù)性動詞有come, go, leave, start, die, finish, become, get married等。

舉例：

I saw this film yesterday.(強調看的動作發(fā)生過了。)

I have seen this film. (強調對現(xiàn)在的影響，電影的內容已經(jīng)知道了。)

句子中如有過去時的時間副詞(如 yesterday, last, week, in 1960)時，不能使用現(xiàn)在完成時，要用過去時。

(錯)Tom has written a letter to his parents last night.

(對)Tom wrote a letter to his parents last night.

句子中如有過去時的時間副詞(如 yesterday, last, week, in 1960)時，不能使用現(xiàn)在完成時，要用過去時。

(錯)Tom has written a letter to his parents last night.

(對)Tom wrote a letter to his parents last night.

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