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

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

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.
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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、应该做某事
2、本应该做某事而没有做