表示情感和态度，含有责备、批评的意味。常作这种用法的情态动词有 could,should/ought to,need:
could + have done, 表示 本可以做却没做...
You could have done better, but you didn't try your best.
They could have let me know they were going to be late!should/ought to + have done, 表示本应该却没有做...
He should have finished the work by now.
You ought to/should have helped him.needn't + have done, 表示不必做却做了...。
You needn't have watered the flowers, for it is going to rain.
You needn't have told them again. I have told them already.
