must have+P.P 与may,might could have +p.p的区别

must have+P.P是表示对过去发生的事情的肯定推测,“一定已经.”的意思.如：I didn't hear the phone,I must have been asleep.(我没听到电话响,那时我一定是睡着了)
may have +P.P.might have +P.P 表示对过去某事做可能性推测,might与may同义,只是其可能性比may更小.如：He is late.He maight have met an accident.(他迟到了,或许出了意外)
could have +p.p通常用否定形式could not have +p.p,或疑问句,表示对过去事情否定或疑问的推测.