could和should的区别用法

　　could的意思为“能够、打算”，should的意思为“应该、将会、可能”。could只能作情态动词使用，should既可作情态动词，又可作助动词使用等。Should 表建议 (advice)、Could 表可能性 (possibility)。

　　1.Should 表建议 (advice)

　　If you want to lose weight, you should eat healthy food.

　　如果你想减肥，你应该吃健康的食物。

　　You shouldn’t spend so much time watching TV.

　　你不应该花这么多时间看电视。

　　My tooth has been hurting for a week already.

　　---You should go to the dentist.

　　2.Could 表可能性 (possibility)

　　I have the day off tomorrow.

　　明天我放假。

　　Great! We could spend the day at the beach. Or we could go shopping.

　　太棒了!我们那天可以去海边。或者去逛街。

　　Could I use your phone, please?(礼貌用语)

　　请让我用一下你的电话可以吗?

　　表示对于过去的假设

　　1.Should Have

　　过去情况的假设，并且也表示“我应该......”，即“过去那个时候，我应该......”

　　I should have left my house earlier.

　　我该早点出门。

　　I shouldn’t have yelled at you yesterday. I’m sorry.

　　我昨天不该吵你吼。对不起。

　　You should have studied. You shouldn’t have played video games all weekend.

　　你该学习。你不应该整个周末都玩电子游戏。

　　2.Could Have done

　　用于描述可能性。即“过去如果怎样/不怎样，现在情况可能有所不同。”

　　(1)是一种虚拟语气的用法，条件从句是过去完成时，主句could+ 现在完成时

　　If I had gone to college, I could have gotten a better job.

　　如果我上了大学的话，我可能会找到了更好的工作。

　　(2)Could have 一般与 “if +过去完成时” (If I had gone)连用-这里的条件句是一种虚拟语气的用法。

　　She could not have been on that flight because I just saw her at work.

　　她不可能

　　(3)有时候，could have 也可不接条件句，单独出现。

　　Are you crazy? We could have gotten into an accident.