be supposed to do sth.被期望做某事,应该做某事,to是不定式符号,不是介词,后应接动词原形,be supposed to常用来表示劝告,建议,告知义务或责任等,相当于should
You are supposed to ask the teacher if you want to leave the classroom.
如果你要离开教室,你要问问老师
在口语中,常用否定结构“be not supposed to do sth.”,意为“不允许做某事,不应该做某事”,相当于shouldn't
You are not supposed to smoke on the bus.=You shouldn′t smoke on the bus.
你不应该在公交汽车上吸烟
be supposed to have done sth.本应该做某事而没有做
You are supposed to have handed in your homework.
你本应该交作业了
supposed+that从句,当变为否定句时,否定词应该前移,类似词还有think,believe等
I don't suppose he well tell you about it.
我认为他不会告诉你这件事
suppose还有“猜想”的意思,suppose sb. to do sth.猜想某人做某事
I supposed him to stay at home
我猜他待在家
如果表示“过去某时应该(不应该)做”时,用was(wasn′t)/were(weren't)supposed to,相当于should(shouldn't)have+动词的过去分词
I was supposed to arrive at7:00,but I arrive at8:00
我应该7点钟到,却在8点钟到