be supposed to的用法
suppose的基本意思是“猜想；以为；假定”，但在具体的语言环境中意义不止于此，其用法如下：
1. suppose + that 从句，表示“猜测；假定”。如：
I suppose that you are right. 我想你是对的。
You can suppose that A equals B. 你可以假定A等于B。
- suppose +名词 / 代词 + to be...，表示“认为……是……”。如：
Many people suppose him to be over 50. 许多人认为他已经50多岁了。
- suppose用于祈使句中，表示“让……”。如：
Suppose we go for a swim. (= Let's go for a swim.) 让我们去游泳吧。
be supposed to 的用法
用法一： be supposed to... 其中to是动词不定式符号，不是介词，其后要跟动词原形。当be supposed to... 的主语是“人” 时，意为“应该…… ”；“被期望……”，它可以用来表示劝告、建议、义务、责任等，相当于情态动词should。如：
Everyone is supposed to wear a seat-belt in the car.
每个人在汽车里都应该系安全带。
Teachers are supposed to treat all the students alike.
老师应该对所有的学生一视同仁。
用法二：当be supposed to... 的主语是“物”时，它表示“本应；本该”，用于表示“某事本应该发生而没有发生”。如：
The new laws are supposed to prevent crime. 这些新法令本应该起到防止犯罪的作用。
The train was supposed to arrive half an hour ago. 火车本应在半小时之前到达。
用法三： be supposed to后面接“have
- 过去分词”时，表示“本应该做某事而没做”。如：
You are supposed to have handed in your homework by now.
现在你应该已经把作业交上来了。
He is supposed to have arrived an hour ago. 他应该一小时前就到了。
用法四： be supposed to... 的否定结构为be
not supposed
to...,它常用于口语中，意为“不被许可；不应当”。如：
She was not supposed to be angry about that. 她本不该为那件事而生气的。
You are not supposed to smoke on the bus. 你不应该在公共汽车上吸烟。
suppose的其他用法：
1．suppose ＋that 引导的宾语从句“假设，猜想，以为”。例如：
Let's suppose that you had a million dollars，how would you spend it?
假如你有一百万美元，你怎么花呢?
I suppose that she'll be there today．
我想她今天能到那里。
I had supposed he had died years ago．
我原以为他几年前就去世了。
2． 当suppose ＋that 引导的宾从变为否定句时，否定应前移，有此种用法的词有think，believe， guess（猜想）等。例如：
I suppose that she will come to your party．
→ I don't suppose that she will come to your party．
我猜她不会来参加你的晚会。
I suppose that he will agree with you．
→ I suppose that he will agree with you．
3． 在表示同意或不同意别人的观点时，常用“I suppose
so/ I don't suppose so”。
－－－ Will he be back this weekend?
他周末会回来吗?
－－－ Yes， I suppose so．
我想他会回来。
