六、shall, should

1. shall用于第一、第三人称疑问句，征求对方意见

2. shall用于第二、第三人称陈述句，表示命令、警告、威胁、允诺等。

He shall end up in prison if he steals like this.

3. 用于所有人称，表示规定、法令、预言等，意思为“必须”。

4. should(ought to)用于表示义务、责任、劝告、建议、命令等，“应该”

5. should have done sth.“本来应该…” shouldn’t have done sth.“本来不应该…”有时有责备的意思。

6. should表示有一定根据的推测或可能性，“应该会…”

He should have got there by now.

7. should在疑问句表示惊讶、不应该等。

8. 用于I should say/advise/think…,等，表示谦虚、婉转。(虚拟语气另讲)

七、had better (not) do sth.

had better (not) do sth. 最好(不)做某事。

八、易错点

1. used to do sth.过去常常做某事

be used to do sth.被/可以用来做某物

be used to doing sth.习惯于做某事

2. can与be able to

均表示“能力”。 be able to有各种时态变化，后不能跟不定式的被动形式。was/were able to do sth.表示过去经过努力做成了某事，不能用could代替was/were able to. could have done表示对过去情况的把握不大的肯定判断或过去本来有可能做但没有做。

3. used to do sth.表示过去的经常发生的动作或状况，暗示与现在不同，可用于无人称句和存在句。would do sth.仅表示过去习惯性的动作，没有与现在对比的含义，不能用于无人称句和存在句。

We would have a walk along the river bank after supper.

There used to be a temple on top of the hill.

4. 情态动词+have+过去分词

It must have rained last night, for the yard is wet this morning.

He can’t have gone left for Australia. I met him in the theater several minutes ago.

They could have gone exploring on their own and lost their way back to the group.

He may/might not have settled the problem.

5. 特定语气、态度：

can: 在否定、疑问、感叹句中表示惊异、怀疑

may: 表示祝愿

should: 表示惊奇、赞叹、惋惜、不满等情绪

must: 表示偏要、硬要

shall: 用于第二、第三人称陈述句，表示命令、警告、威胁、允诺

九、惯用法

1. cannot…too/enough 无论怎么…也不过分

2. cannot but do sth. 不得不…，只好…

3. may well do(原形)与may as well do sth. 见前面“二5”.

4. would rather do sth.(than do sth) 宁愿...(也不愿...)

would like sth.想要某物

would like to do sth. 想要做某事

prfer to do sth 宁愿做某事

prfer to doing sth.(to doing sth.)/would do sth than do sth./prefer to do sth rather than do sth.宁愿...(也不愿...)

prfer sb. to do sth/would rather sb. did sth. 宁愿sb.做某事

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