Past May, might and could + perfect infinitive express uncertainty with reference to past actions:
{"Image DocumentName": "PastMay, might and could + perfect infinitive express uncertainty with reference to past actions:", "Image ImageDescription": "We haven t heard from him for ten years. He may/might/could have died. (Perhaps he has died, but we don t know.)But when we want to say that something was possible but did not happen, we use might or could: He was very careless when crossing the road. He might/could have died. (He didn t die.) I could have caught the bus if I had hurried. (I didn t hurry, so I didn t catch the bus.) Couldn t + perfect infinitive is often used with comparative adjectives: It was a great year, and I couldn t have been happier. (I was very happy) May/might not + perfect infinitive is used for uncertainty, but could not + perfect infinitive (except for the case above) expresses deduction: I had better call Anne. She may/might not have read my  . (uncertainty) It couldn t have been John you saw this morning. He is away on holiday. (deduction)", "Image XResolution": "37", "Image YResolution": "37", "Image ResolutionUnit": "Pixels/Centimeter", "Image Software": "SlidePlayer", "Image YCbCrPositioning": "Centered"}