(1)主句中有一些成分被省略

　　(I'm)Sorry to hear that you are ill.

　　(It is a)Pity that he missed such a good chance.

　　(2)省略了一个从句或从句的一部分，用so或not(切不可用it或that)代替。

　　-Is he coming back tonight?

　　-I think so.

　　-Is he feeling better today?

　　-I'm afraid not.

　　这种用法常见的有：How so？Why so？Is that so？I hope so.He said so.及I suppose not.I believe not.I hope not.等。(但I don't think so.比I think not.更常用)。

　　4．其他省略

　　(1)连词that的省略：

　　①在宾语从句中that可省略，但如果有两个或两个以上的宾语从句时，除第一个that外，其他that不能省略。

　　He said(that)he had arrived here two days before and that he had lived in a hotel.

　　②定语从句中，作宾语的that，which或whom可以省略。

　　The book(that)he bought yesterday was expensive.

　　(2)不定式符号to的省略

　　①并列的不定式可省去后面的to。

　　I told him to sit down and wait for a moment.

　　②某些使役动词(如let，make，have)及感官动词(如see，watch，notice，hear，feel，look at和listen to等)后面作宾语补足语的不定式一定要省去to，但在被动语态中须把to复原。

　　I saw the boy fall from the tree.

　　The boy was seen to fall from the tree.

　　③介词but前若有动词do，后面的不定式不带to。

　　The boy did nothing but play.

(3)在某些状语从句中的省略