Grammar      modal  verbs in the past    

  must have + p.p , can't have + p.p , might have + p.p

We use must have when we have a good reason for thinking that something in the past is true

The lights are off. He must have gone out.

الانوار مطفاة. لابد( من المؤكد ) انه رحل

He didn't answer the phone. He must have been asleep

لابد( من المؤكد ) انه كان نائما. . فهو لم يرد على الثليفون

I saw him driving a new car .He must have bought it recently.لقد رايته يقود سيارة جديدة من المؤكد ان اشتراها حديثا          

We use can't have when we have a good reason for thinking that something in the past is not true.

Tunneling under the Nile cost much money. It can't have been cheap.ان حفر نفق تحت النيل يكلف مالا كثير. من المؤكد ان هذا لم يكن ابدا رخيصا                       

He has scored three goals .He can't have been bad player

لقد احرز ثلاثة اهداف . من المؤكد انه لم يك  لاعبا سيئا         

We use might have with the possibility of being something true  

I'm not sure .He might have gone to work