谓语动词无论怎么变，算一个整体
以时间和情态为划分，共16个
8中时间： 过去，现在，将来，过去将来
8中情态：一般，进行，完成，完成进行
常用8种
一般过去 一般现在 一般将来 一般过去将来 过去进行 现在进行 过去完成 现在完成
| 时态 | 过去 | 现在 | 将来 | 过去将来 |
|---|---|---|---|---|
| 一般 | ||||
| 进行 | ||||
| 完成 | ||||
| 完成进行 |
动词变成过去式 did / was / were
Last year Japan experienced 2,125 incidents of school violence.
this city was one of the largest human settlements in the world.
动词使用动词原型，do / does
表示现在的状态
So far the results are inconclusive.
Today it makes almost no difference.
Pearson also predicts a breakthrough in computer-human links
表示现在经常性习惯性的事情
But most law graduates never get a big-firm job.
Archaeologists commonly use computers to map sites and the landscapes around sites.
表示现在的将来
will +do OR am/is/are going to + do
We will have a less civil society.
I don't know if other clients are going to abandon.
the problems will be different.
Clearly, only the biggest and most flexible television companies are going to be able to compete in such a rich and hotly-contested market.
站在过去，看之后要发生的事情
would +do OR was/were going to +do
They gave justices permanent positions so they would be free to upset those in power.
it simply didn't foresee what would happen next.
For a while it looked as though the making of semiconductors ... was going to be the next casualty.f
强调过去的时候正在进行
was/were +doing
He was searching for tiny engraved seals.
Within two weeks, he was talking for the first time with the board of Hartford Financial Services Group.
强调现在正在进行
am/is/are +dong
Home prices are holding steady in most regions.
Every cat with an owner.. is running a small-scale study in operant conditioning.
站在过去的时间点，回头往之前看，无论做完没做完，即过去的之前
had + done 过去分词
He had never gambled before the casino sent him a coupon for $20 worth of gambling.
The interviewers had rated applicants on a scale of one to five.
He expressed the opinion that in two or three respects his mind had changed during the preceding twenty or thirty years.
Roman Catholicism had been the state religion....
表示现在已经全部完成或部分完成
截止到现在的时间点，回头往之前看，看看事情完成的结果如何， 即现在的之前
have / has + done
Time ... has given them legitimacy.
The ethical judgements of the Supreme Court justices have become an important issue recently.
For the most part, the response has been favorable.
加修饰词表示现在完成时
Most leading retailers have already tried e-commerce with limited success, and expansion abroad.
Families have also experienced changes these years.
宏观上，时间段不同
the response has been favorable 从过去到现在都赞成
the response was favorable 过去赞成
现在全部完成，可以换成过去时
He has left, so I cannot find him now. 使用时间点强调为现在完成时
He left two hours ago.
部分完成，不能换成过去时
We have learned English for 15 years.
We learned English for 15 years.
截止到将来的时间点，往回看
will have +done （have必须是原型）
relaxation will be in front of smell-television, and digital age will have arrived.
当前时间点之前，强调进行的过程
have been +doing
We have been working hard for several months.
That kind of electronic spying has been going on for decades.
Bankers have been blaming themselves for their troubles in public.