should是shall的过去式，作为情态动词时，则表示“应该～”。
1) would的用法（请记住以下几个句型）
Would you have a cup of tea？可以请你喝杯茶吗？
1.Would you～？和Will you～？
这两个句型皆表示客气的请求、劝说……，但Would you～？更客气些。
Would you tell me the way to the station？
劳驾，您能告诉我去车站怎样走吗？
（回答同《Will you～？》句型）
2.主语+would like to～
表示“想要……”的意思上，与…want to～意思一 样，但用此句型较客气。
I want to ask you a question.
=I'd（I would）like to ask you a question.
我想问你一个问题。
3.Would you like～？
表示请求、劝说，是很客气的说法。
Would you like a cup of tea？
您愿意喝杯茶吗？
Would you like to sing a song？
请唱首歌好吗？
注意
I'd读为〔aid〕
=I would
=I should
=I had
2) should的用法
You should read this book.你应该读这本书。
1.should（应当、应该）用于所有人称，与ought to～同义。
You should wait a little more.
=You ought to wait a little more.
你应该再多等一会儿。
2.在表示要求、命令时，语气是由should（应该）、～had better（最好）、～must（必须）逐渐加强。
had better
had better相当于一个助动词，它后面要跟动词原形；had better只有一种形式，没有has，have better这一形式；它的否定式是在它后面加not。
You had better go now.你最好现在走。
He'd（=He had）better do it now.他最好现在做。
She'd better not cry.她最好别哭。
