[英语语法手册]情态动词--should
should
情态动词Should表示"劝告"、 "建议 "时
这时should常译作 "应当"。如：
We Should learn about the computer and make full use of it.我们应该了解计算机并加以充分利用。
You should listen to the doctor's advice.你应当听大夫的话。
You should study the article care fully. 你应当细，心学习这篇文章。
should还可以表示 "预测"、"可能"
They should be here by now.他们现在可能到了。
The reference book should be in the reading-room.这本参考书可能在阅览室里。
should有时表示说话人的感情如惊奇、愤怒、失望等
Why should I go? 我干吗要去?(不满)
I am sorry that he Should be so obstinate.我很遗憾，他竟这样固执。(失望)
It's strange that it should be so hot today.很怪，今天怎么这么热。(惊奇)
should后跟动词的完成式时
这时句子指的是过去的事情。如果是肯定句，常说明某件事本应完成而未完成；如果是否定句，表示发生了不应当发生的事情.如：
You should have stopped at in red light. 你见了红灯本应该停车。
You Should not have gone back to work without the doctor's permission.你不应当未经医生许可就回去工作。
He Should have come earlier. 他应早一点来。