現在完成時for和since的用法解釋及分析

For和since都表示我們說到的時間從過去開始一直持續到現在，但是for與since不能混用。

例如：

“I have lived in Italy for 13 years.”

“I have lived in Italy since 2003.”

當我們用for的時候，表示一個活動持續一段時間，從過去到現在。

我們用since的時候，表示過去的行爲開始一直持續到現在。

兩句話有同樣的含義。for的例子中用了“13年”這個時間，但由於 2003年加上13年就是2016年，即今年。兩句話的`重點都是現在，“我”繼續住在意大利，沒有去其他國家。

Since用來說明動作起始時間，for用來說明動作延續時間長度。

給大家舉一些例子, 什麼時候該用for和since

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.

但是並非有for 作爲時間狀語的句子都用現在完成時。

I worked here for more than twenty years.

(我現在已不在這裏工作。)

I have worked here for many years.

(現在我仍在這裏工作。)

當現在完成時+一段時間，這一結構中，我們用下面的公式轉化，很容易就能排除非延續動詞在完成時中的誤使。

1) (對)TomhasstudiedRussianforthreeyears.

=TombegantostudyRussianthreeyearsago,andisstillstudyingitnow.

2) (錯)Harryhasgotmarriedforsixyears.

=Harrybegantogetmarriedsixyearsago,andisstillgettingmarriednow.

顯然，第二句不對，它應改爲Harrygotmarriedsixyearsago. 或Harryhasbeenmarriedforsixyears.