Hi how are you..? please could you help and guide me to the right answer? I was watching a movie and in that scene a boy tried to kill his mother and she want to protect him no matter what..someone killed the boy then the mother cried and blamed him for what he did.{ After what happened he said : he was gonna to kill her} and his friend said to him{ She would have died to see him live} My question is why he didn't use could have instead of would?? I was googling I found in Yahoo answer this answer here: https://answers.yahoo.com/question/index?qid=20180425143843AAZ05UH
You are describing here two different situations, which require two different verbs. In situation 1 (the mother in the movie), the verb 'would' is correctly used. 'Would have' expresses a sense of will, or a desire to make something happen. In situation 2 (the car accident in Yahoo), 'could have' expresses a possibility that is outside the subject's control. woofgang's answer is correct.
grammatically could comes from the verb can - to be able, would comes from the verb will - to choose to make something definitely happen
He would have died - a definite unless..
He could have died - only a possibility