 Past modals should have, could have, and would have. Should have, could have, and would have are sometimes called modals of lost opportunity because they describe situations when we are imagining that the past was different. Before we study those terms in the past, let's review the difference between should, could, and would. The general rule is, use SHOULD for recommendation or advice. For example, if you want to lose weight, you should eat healthy food. Use COULD for possibilities. For example, I have the day off tomorrow. Great! We could spend the day at the beach, or we could go shopping. And use WOULD for imagining results. For example, if I were rich, I would buy a boat. The same general rule applies when using SHOULD HAVE, COULD HAVE, and WOULD HAVE for imaginary past situations. Use SHOULD HAVE to say that a different action was recommended in the past. If you arrived late to English class, you can say, I should have left my house earlier. If you now regret an argument, you can say, I shouldn't have yelled at you yesterday. I'm sorry. You can also use SHOULD HAVE or SHOULDN'T HAVE to tell other people that a different action in the past would have been better. If your son failed a test, you can say, you should have studied. You shouldn't have played video games all weekend. Use COULD HAVE to talk about possibilities if something had been different in the past. For example, someone who didn't go to college can say, if I had gone to college, I could have gotten a better job. When talking about a gymnast who didn't win a competition, you can say, she could have won the gold medal if she hadn't fallen three times. COULD HAVE is often used with IF plus HAD plus the past participle, if I had gone, if she hadn't fallen. These IF phrases express the imaginary past situation, and then COULD HAVE expresses the possible results. But you can also use COULD HAVE to express past possibilities without specifically saying the IF phrase. Imagine you're driving with a person who made a dangerous maneuver on the road. You can say, are you crazy? We could have gotten into an accident. COULD HAVE is for possibilities, but WOULD HAVE is for results. Use WOULD HAVE to imagine a result if something had been different in the past. For example, if you arrived late at the airport and missed your flight, you can say, if we had arrived earlier, we would have caught our flight. If you forgot your umbrella and it started to rain and you got wet, you can say, if I had brought my umbrella, I wouldn't have gotten wet in the rain. WOULD HAVE expresses more certainty about the result than COULD HAVE. For example, if you say, if I had worked harder, I could have gotten a promotion, you're saying it was a possibility. Maybe I'd get a promotion, but maybe not. But let's consider a test where you need 70% to pass and you got a 68. I got a 68 on the test. If I had gotten two more points, I WOULD HAVE passed. WOULD HAVE expresses more certainty. With the two extra points, passing the test was certain. In spoken English, many people say SHOULD HAVE, COULD HAVE, and WOULD HAVE. Click on the link in the video or in the description for more information about my advanced English grammar course, which will help you improve your English. It contains 45 detailed lessons, plus writing tasks with teacher feedback.