何时用现在完成时，何时用一般过去式？

1. 现在完成时和一般过去时都表示在过去完成的动作, 但现在完成时强调这一动作与现在的关系, 如对现在产生的结果、影响等，而一般过去时则表示动作发生在过去，一般不表示和现在的关系。试比较：

① Who has opened the door?谁把门开了？（现在门还开着）

Who opened the door? 谁开的门？ (指过去，与现在无关。现在门是关着还是开着，没有说明。)

② — Have you had your lunch?你吃过午饭没有？ （意即你现在不饿吗？）

— Yes, I have. 吃了。（意即我现在饱了，不要再吃了。）

— When did you have it? 你什么时候吃的？ （说话人感兴趣的是“吃”这一动作发生在什么时候。）

2. 一般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, once, last week, ... ago, in

1980, in October, just now等具体的时间状语。

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/last years, always等不确定的时间状语。

共同的时间状语：

this morning, tonight, this April, now, ever, before, already, recently, lately等。

3. 现在完成时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等。

过去时常用的非延续性动词有come, go, leave, start, die, finish, become, get married等。 eg.

① 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。)

② He has been in the League for three years. (在团内的状态可延续)

He has been a League member for three years. (是团员的状态可持续)

He joined the League three years ago. (三年前入团，joined为短暂行为。)

句子中如有一般过去时的时间状语（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.