Past Modals

Form

I should have studied harder.

He might have been asleep.

You shouldn’t have eaten so much.

We use might have, may have, and could have to speculate or make a guess about a past event. We are not sure what happened.

might have / may have: A past possibility. (e.g. 30-50% certain)

“Why didn’t he call?” “He might have forgotten.”

could have: Suggests one of several possibilities. Also used for a past opportunity that was not taken.

(Speculation): The police are not sure how the fire started. It could have been an accident.

(Lost opportunity): You could have gone to university, but you decided to travel instead.

couldn’t have: Certainty that something was impossible in the past.

She couldn’t have stolen the money; she was with me all day!