might - Used for saying that there is a possibility that something is true, or that something will happen, specially when it is not very likely. eg- You never know what might happen in the future. -Used for asking for or giving permission -Used for very politely asking permission to do something. eg- I wonder if i might use your book. -Used for making a suggestion. eg - I thought we might have a walk round the town. -Used for saying that someone did something in order to achieve a particular purpose. eg- He refused an invitation so that he might spend sunday with you.

Could have been - We use could have been to talk about a present possibility that hasn't happened yet. And we use it before an -ing verb. Example -: He could have been earning a lot but the work was too hard. He could have been at party but you didn't notice.