This is Everyday Grammar. I'm Kaveh.
欢迎收看《每日语法》栏目，我是卡维。
Past tense modals are useful for expressing your present feelings about a past decision.
过去时态的情态动词对表达一个过去决定的现在感觉很有用。
Wait a minute. I didn't introduce myself!
等一下。我还没自我介绍呢！
I'm sorry. It's true, you could have introduced yourself.
抱歉。你本可以自我介绍的。
Well, since you already gave a clever example of the modal Could Have,
好吧，既然你已经给出了一个不错的情态动词Could Have的例子，
it's important to let our viewers know that Could Have and Would Have are sometimes called "modals of lost opportunity."
那么重要的是，让我们的观众知道Could Have和Would Have有时被称作“失去机会的情态动词”。
Could Have means that something was possible in the past, but it did not happen.
Could Have的意思是某事过去有可能发生，却没有发生。
I could have travelled the world, but I never got a passport.
我本可以环游世界，但我没护照。
To form the negative, just add not between could and have.
要构成否定式，只需在could 和 have之间加一个not。
I means that something was impossible in the past.
意思是某事过去不可能发生。

I could not have travelled the world, because I never got a passport.
我过去不可能环游世界，因为我没护照。
Would Have is a bit more complicated since it has two common meanings.
Would Have就有点儿复杂了，因为它有两个常用含义。
But we will only talk about the one that shows how you wanted to do something in the past, but you could not.
但我们只讨论一个，即你过去想做但没做某事的含义。
Here, you use But, as in: I would have A, but I had to B.
这里，你要用到“But”了 ,句式是， I would have A, but I had to B（我本可以有A，但我只有B）
I would have called, but I had to work.
我本可以打电话，但我得工作。
The structure for both modals is easy to remember.
这两个情态动词的结构很容易记。
Just use Could/would+have+past participle verb
即：Could/would+have+动词的过去分词
Use have for all pronouns.
所有的代词都用have。
Never use has or had to form a past modal.
不要用has或had构成过去时态的情态动词。
And remember: use Could Have when something did not happen.
记住： Could Have是在某事没发生时使用。
And use Would Have when something could not happen.
Would Have是某事不可能发生时使用。
And that's Everyday Grammar.
以上就是今天的全部内容。