对动词加上完成元素

Present perfect tense

The time of the action is before now but not specified, and we are often more interested in the result than in the action itself.

我主要把握以下5点它的使用场景：

An action or situation that started in the past and continues in the present. I have lived in Bristol since 1984 (= and I still do.)
An action performed during a period that has not yet finished. She has been to the cinema twice this week (= and the week isn’t over yet.)
A repeated action in an unspecified period between the past and now. We have visited Portugal several times.
An action that was completed in the very recent past, expressed by ‘just’. I have just finished my work.
An action when the time is not important. He has read ‘War and Peace’. (= the result of his reading is important)

现在完成时态是写作中常用的时态，我要重点把握住它。

Past perfect tense

这个时态的主要作用就是来描述2个过去发生动作的先后。It does not matter which event is mentioned first - the tense makes it clear which one happened first.

例句：I had saved my document, before the computer crashed.

我们假设保存文档是事件A，电脑崩溃是事件B，上面的时态已经清晰地表明了事件A发生在事件B之前。

这个时态还有另一个用途就是在 reported speech 中。

例句：Jane said that she had gone to the movies.

由于我不经常做报告演讲，显然这个时态的这种用途对于我来说没什么大作用。我应该重点把握的就是第一种用途。

对动词同时加上完成和进行时（ing）元素

Present perfect continuous

下面是普渡大学的说法：

To express duration of an action that began in the past, has continued into the present, and may continue into the future.

下面是英孚的说法：

The present perfect continuous is used to refer to an unspecified time between ‘before now’ and ‘now’. The speaker is thinking about something that started but perhaps did not finish in that period of time. He/she is interested in the process as well as the result, and this process may still be going on, or may have just finished.

下面是英孚给出的这个时态描述的2种情况：

actions that started in the past and continue in the present

She has been waiting for you all day (= and she’s still waiting now).
I have been working on this report since eight o’clock this morning (= and I still haven’t finished it).
They have been travelling since last October (= and they’re not home yet).

actions that have just finished, but we are interested in the results

She has been cooking since last night (= and the food on the table looks delicious).
Someone has been eating my chips (= half of them have gone).
It has been raining (= and the streets are still wet).

看了很多经济学人的文章，感觉这个时态没有现在完成时态常用。那么我应该如何在它与现在完成时之间进行选择呢？其实不难看出，英孚给出的2种情况完全都可以理解为一个动作发生在过去，一直到现在，然后在未来可能也会继续发生。因此总结来说，当我想要描述的动作发生在过去，一直到现在，然后在未来可能也会继续发生，应该选择完成进行时态，也就是普渡大学的说法。

Past perfect continuous

我们已经理解了过去完成时（主要描述2个过去发生动作的先后），我们在现在完成进行时章节中理解了进行元素的含义。因此总结来说，过去完成元素总会涉及到2个事件，即对应2个时间点，这个时态本身已经清晰地表明了2个事件的先后，暂且称先发生事件为A，后发生事件为B。然后加了进行元素以后，它就表明了事件A的动作一直持续到事件B的发生，可能会继续发生，在事件B的时间点以后。

例句：We had been trying to open the door for five minutes when Jane found her key.

我假设称试着开门为事件A，找到钥匙称为事件B. 因此上面的句子中有2个在过去的时间点。由于加上了进行元素，因此我们可以把这句话解释成事件A一直持续到事件B的时间点，可能会继续发生，在事件B的时间点以后。当然了生活常识告诉我们事件A不能发生下去了，因为钥匙找到了，谁还会继续试着去开门。

下面的3个句子你完全都可以用我上面介绍的逻辑来理解：

Had you been waiting long before the taxi arrived?
It had been raining hard for several hours and the streets were very wet.
Her friends had been thinking of calling the police when she walked in.

上面是我自己总结的想法，而下面是英孚的说法：

The past perfect continuous corresponds to the present perfect continuous, but with reference to a time earlier than ‘before now’. As with the present perfect continuous, we are more interested in the process.

如果有些句子用我的那个方法解释不通，可以用这个试试。

容易混淆的2组动词时态

本小节所有总结的内容来自于 Coursera MOOC: Grammar and Punctuation

Present perfect VS Present perfect progressive

大多数时候，这2个时态的意思相同，用哪个都可以。比如下图中的例句：

但是在某些时候，只有一种时态是正确的。比如下图中的3个例句，这3个例句的原因分别是：1）Be 动词 are not usually used as main verbs in present perfect progressive. 2）Before is a time signal that means this action is finished。So you can’t use present perfect progressive. 3）现在完成进行时用来 emphasize that the action is still going on, when you see for some period of time, you’ll know you should use present perfect progressive.

The picture below are some of the signal words to tell you which verb tense you should use. There could be some exceptions, but in general, the words on the left will signal present perfect, and the expressions on the right will signal present perfect progressive.

Present Perfect VS Simple Past

If an action that happened and finished at a specific time in the past, you should use simple past tense; If an action that happened at a nonspecific time, and may even continue to now, you should use present perfect tense.

下图中分别是2个动词时态的关键词：

其实在很多句子中并不会出现上图中的关键词，这时我们需要用上面给出的文字描述来判断用哪个时态，其实从描述中可以发现，现在完成时主要强调的是 now 这个时间点，now 很重要，但是动作发生在具体的过去的哪个时间点并不重要; 而一般过去时正好相反，它最关注的是过去的某个时间点。2种时态的比较如下图所示：

参考资料

Verbs

Active Verb Tenses

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