比較since和for

Since 用來說明動作起始時間，for用來說明動作延續時間長度。

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 作為時間狀語的句子都用現在完成時。

I worked here for more than twenty years.

(我現在已不在這里工作。)

I have worked here for many years.

(現在我仍在這里工作。)

小竅門：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) Tom has studied Russian for three years.

= Tom began to study Russian three years ago, and is still studying it now.

2)(錯) Harry has got married for six years.

= Harry began to get married six years ago, and is still getting married now.

顯然，第二句不對，它應改為 Harry got married six years ago.或 Harry has been married for six years.