could have done可以表示「過去本來能夠做某事而實際上沒有做」。如：
i could have come here a little earlier,but im late because of the bad traffic
must have done表示對過去已經發生過的情況的肯定推測，語氣較強。
擴展資料。
may / might have done表示對已經發生過的情況的.肯定推測，語氣稍弱。might have done還可表示「本可能做某事而實際上沒有做」。如：
she didn''t come on time.she may / might have missed the bus
he might have given you more help,but he was very busy then
should / ought to have done表示「本該做某事而實際上沒有做」，其否定形式表示「本不該做某事而實際上做了」，通常含有責備的意思。如：
the flowers have died.i should / ought to have watered them often
you shouldn''t / ought not to have told them the truth
i could have come here a little earlier,but im late because of the bad traffic
must have done表示對過去已經發生過的情況的肯定推測，語氣較強。
擴展資料。
may / might have done表示對已經發生過的情況的.肯定推測，語氣稍弱。might have done還可表示「本可能做某事而實際上沒有做」。如：
she didn''t come on time.she may / might have missed the bus
he might have given you more help,but he was very busy then
should / ought to have done表示「本該做某事而實際上沒有做」，其否定形式表示「本不該做某事而實際上做了」，通常含有責備的意思。如：
the flowers have died.i should / ought to have watered them often
you shouldn''t / ought not to have told them the truth