be supposed to do sth与should have done sth 有什么区别？急急急！！谢谢

be supposed to do sth与should have done sth 有什么区别？急急急！！谢谢

should have done sth的sth比be supposed to do sth的sth更贴近现实,是客观正确该做的事
be supposed to do sth的事情只是理论上应该做的事,有可能是依照常理该做的,依照他人的命令该做的,是在某人主观观念中正确的事.
还有不解请追问

第一个是 应该做... 第二个是 本应该做什么却没有 比如 JACK FAILED THE EXAM,HE SHOULD HAVE DONE BETTER.

1.be supposed to do= should do 应该做某事： you are supposed to go to school on time=you should go to school on time. 你应该按时上学。 2.be supposed to have done sth= should have done. 应该做成了某事（实际上没做成）： you are supposed to have done your homework= you should have done your homework. 你本应该能完成作业的。