英语中助动词should, would的用法

助动词：辅助其他动词构成时态、语态、疑问句式、否定名式的动词。助动词有些词义，有些没有词义，或者暗含一点词义。放在谓语首位置助动词会受主语人称、数的限制，其他位置不会受限制。

should, would用来表示过去将来时态，should用于第一人称，would用于第二、三人称(在美国也可用于第一人称)：

I said I should turn in the exercise book the next day.

我说我将在第二天交作业本。

He asked whether they would come back that evening.

他问他们是否当天晚上回来。

should和would常用于虚拟语气中：

If it should rain tomorrow, I would stay at home.

如果明天下雨，我会待在家里。

If he should come back, we would welcome him.

要是他回来，我们会欢迎他。

Put on your raincoat in case it should rain.

穿上雨衣，以防下雨。

should表示惊讶和“应该”：

It surprised us that he should have failed in the test.

他竟然测试没过关，我们感到很惊讶。

Why should he have made such a big mistake?

他怎么会犯这么大的错误呢?

You should have informed me two days in advance.

你们应该提前两天通知我。

We should learn from and help each other.

我们应该互相学习，互相帮助。

would常用于委婉、客气地提建议、请求：

Would you help me serve tea?

你帮我上荼好吗?

What would you like to eat?

你想吃点什么呢?

I’d like some vanilla ice-cream.

我想要些香草冰淇淋。

would同will一样常用于表示习惯或者倾向：

When she was free, she would go shopping.

她有空时就会逛商店。

When asked a very simple question, he would laugh it off.

当有人问他一个很简单的问题时，他会一笑了之。