We can use may, mightand couldto talk about things that are possible in the present and future.
∑ Where's Fred? He's not in his office.
He maybe in the bathroom... or he mightbe in the conference room.
∑ Don't eat that mushroom. It couldbe poisonous.
∑ The weather forecast says it mayrain tomorrow.
∑ Your daughter is really smart. She couldbe very successful someday.
∑ We mighttake a road trip this weekend.
Some people say that mightis less certain than may,but in spoken English there is really no effective difference. Itís probably best to use might.The word mayis less common, and we can only use couldin the positive form, not the negative form, for talking about possibility:
∑ Are you sure that's a good idea?
The boss may not / might notlike it when he finds out. The boss could notlike it when he finds out.
∑ I may not /might notbe the smartest person in the class, but I definitely work the hardest.
I could notbe the smartest person in the class, but I definitely work the hardest.
When talking about past possibilities, we can use... might have / may have / could have + past participle(for positive possibilities) and might not have / may not have + past participle(for negative possibilities).
Positive Past Possibilities:
∑ She's not home. She might havegone to the store.
∑ He may havemisunderstood you when you talked to him yesterday.
∑ The person who stole the
documents could havebeen one of the employees.
Could haveis usually used in unreal conditions -
when we are imagining a possibility if something in the past had been different: "If we had started this project earlier, we could havefinished on time."
Negative Past Possibilities:
∑ Johnís not here. He might not haveknown about the meeting.
∑ If she hasnít called you back, she may not havelistened to your voicemail yet.
Remember that couldn't haveis only used when we are certain that something is logically impossible in the past:
∑ She couldn't havetaken the car; she doesn't have a key.
∑ Use must(present) and must have(past) when you are very certain that something is/was true
∑ Use can't(present) and couldn't have(past) when you are very certain that something is/was impossible
∑ Use should/shouldn't(present) and should have / shouldn't have(past) to talk about things you expect to be true, although you don't have complete certainty
∑ You can also use should have / shouldn't havefor judging actions in the past to be good or bad
∑ Use might(most common), may,or couldto talk about present and future possibilities
∑ Use might have, may have,or could haveto talk about past possibilities
∑ For a possibility that something did NOT happen, use might not haveand may not have
Youíve finished Lesson 10! Now take the quiz and do the practice exercises to review the modals in todayís lesson.