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Here we’ll look at another difficult issue with verb tenses. In the examples you just saw, you should have used present perfect in the first sentence, because it is talking about an action that was finished before that moment. We say that now is important in that sentence. In the second sentence, you needed simple past because the action happened at a specific time in the past, on Friday. Let’s look at some more examples. The first sentence here uses present perfect. Your key word is all week. This means that it has been happening in the past week, and may continue to now. Because now is important in this sentence, we need present perfect, not simple past. In the second sentence, we use simple past because of the keyword yesterday. Remember simple past is about an action that took place at a specific time in the past and is finished. In the third sentence, we use simple past again because we have this specific time, 3 o’clock. This action started and finished in the past at a specific time. On the next one, we use present perfect because we have the key word five times so far. When you have one time or two times, that’s a key word. So far is also a key word for present perfect, because this means that this action has happened at sometime in the past and may continue. It’s also at a non specific time, which is what present perfect is used for. In the last sentence we also use present perfect. This is the negative. We use present perfect here because of the keyword since. Since Friday or since yesterday, that’s going to indicate present perfect. This means that the action may continue to now. So when now is important, if the action is related to something that happened before now, you will use present perfect. If the action happened in the past, and it’s finished, then you use simple past. Also, again, if the time is not specific in the past, it’s present perfect. If it’s at a specific time in the past, it’s simple past. Here are some of the key words to help you decide between simple past and present perfect. On the left, these are key words for present perfect. These words will help you see that the action was at a non specific time in the past, and may even continue to now. On the right we have keywords for the simple past. These will indicate that the action happened at a specific time in the past. Try another exercise and be sure to look for key words. Let me explain the answers in the exercise you just did. In the first sentence, we used simple past because this action happened in the past and was finished in the past. And we have the key word, an hour ago. In the second sentence we used the present perfect, this is the negative and we have the keyword yet, but we also know this should be present perfect because this is something at a non-specific time in the past that may still continue to now. In the third sentence, we use present perfect because we have the key word since. This is an action that happened in the past, but continues to now. Keep in mind these key words are just clues, not every sentence has them. If there’s no key word, the speaker or writer has to decide if he’s talking about an action that happened and finished at a specific time in the past, or an action that happened at a nonspecific time, and may even continue to now.