比较过去时与现在完成时

1)过去时表示过去某时发生的动作或单纯叙述过去的事情，强调动作;现在完成时为过去发生的，强调过去的事情对现在的影响，强调的是影响。

2)过去时常与具体的时间状语连用，而现在完成时通常与模糊的时间状语连用，或无时间状语。

一般过去时的时间状语:

yesterday, last week，…ago, in1980, in October, just now, 具体的时间状语

现在完成时的时间状语

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

3)现在完成时可表示持续到现在的动作或状态，动词一般是延续性的，如live, teach, learn, work, study, know.

过去时常用的非持续性动词有come, go, leave, start, die, finish, become, get married等。

举例：

I saw this film yesterday.(强调看的动作发生过了。)

I have seen this film. (强调对现在的影响，电影的内容已经知道了。)

句子中如有过去时的时间副词(如 yesterday, last, week, in 1960)时，不能使用现在完成时，要用过去时。

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

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

句子中如有过去时的时间副词(如 yesterday, last, week, in 1960)时，不能使用现在完成时，要用过去时。

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

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