现在完成时for和since的用法解释及分析

For和since都表示我们说到的时间从过去开始一直持续到现在，但是for与since不能混用。

例如：

“I have lived in Italy for 13 years.”

“I have lived in Italy since 2003.”

当我们用for的时候，表示一个活动持续一段时间，从过去到现在。

我们用since的时候，表示过去的行为开始一直持续到现在。

两句话有同样的含义。for的例子中用了“13年”这个时间，但由于 2003年加上13年就是2016年，即今年。两句话的`重点都是现在，“我”继续住在意大利，没有去其他国家。

Since用来说明动作起始时间，for用来说明动作延续时间长度。

给大家举一些例子, 什么时候该用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。)

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)TomhasstudiedRussianforthreeyears.

=TombegantostudyRussianthreeyearsago,andisstillstudyingitnow.

2) (错)Harryhasgotmarriedforsixyears.

=Harrybegantogetmarriedsixyearsago,andisstillgettingmarriednow.

显然，第二句不对，它应改为Harrygotmarriedsixyearsago. 或Harryhasbeenmarriedforsixyears.