shall和should用作助动词时，should是shall的过去式；用作情态动词时，shall和should是两个不同的词，希望同学们对这两个词的用法加以区别。
shall的用法
（1）shall表义务，表示说话人的允诺、命令或威胁，用于第二、第三人称
You shall do as you see me do.
你照我的样子办
Tell her that she shall have the book tomorrow.
告诉她明天可以得到那本书
（2）shall表征询意见，与第一、三人称连用，并用于疑问句
What shall we do this evening？Shall we go to the theatre？
我们今晚干什么？去看戏好吗？
Shall she come right now？
马上要她来吗？
（3）表示决定和决心，用于第一人称
I shall come if I want to.
我想来的话，我就来.
should的用法
（1）should表义务，可用于各种句式，通常指将来
You should do what your parents tell you.
你应该按照你父母的话办
He should do some work, but he doesn't want to.
他应该做些工作，但是他不想做.
（2）should用于完成式时，用于肯定句，表应完成但未完成的动作
He looks very ill. He should have stayed at home.
他看样子病得很严重，本应该待在家里
should用于否定式，表不应完成但已完成的动作
They shouldn't have concealed it from us.
他们本不应该对我们隐瞒那件事
（3）should表推测，暗含很大的可能
Three weeks should suffice
三个星期可能足够了
（4）should可在某些从句中，表虚拟语气
I suggest that you should stay here as if nothing had happened.
我建议你应该待在这儿，好像什么事也没有发生.
（5）should表感情色彩，常用在以why，how开头的疑问句中
Why shouldn't you invite him?
为什么你竟不邀请他？
must，should与ought to三者均可表示义务，但是must的用法最强烈，有“必须”的意思，而should和ought to则有“应当”的意思。
should，ought to与was/were to 用于完成式的比较：
should+完成式与ought to+完成式表所期望的动作未完成，was/were to+完成式则表所计划的动作未完成
You should have helped him.
你本该帮助他的.
He was to have arrived last week
他本该上周到的.
练习题
1、--____ we go out and play today？
--Sorry, too much homework. I ____ go until it is done.
A. Shall，will B. Shall，won't
C. Can，shall D. May，must
2、--We quarreled with the waiter about the bill.
--How silly！You ____ to the manager
A. would have talked B. should have talked
C. could talk D.must talk
答案
1、B
2、B
