if

1. if有时作“即使”解。例如：If he is old, he is at any rate strong. He has read widely, if superficially. 和I will do it if it kills me!

2.有些书里说if不该用作whether解，如I asked him if he knew her。其实这种用法很合习惯。但有下面两点该注意：

（1）if...or not除了在美国口语里以外，现在不普通，如最好不说I asked him if he knew her or not。可以把or not删去或把if改作whether。

（2）把if用作whether解有时会引起误解，如Write to tell me if I am to come可能有两个意思：“写信告诉我我是否应该来。”或“写信告诉我，假使我应该来。”

3.比较下面两句：

• I asked him if he knew her. （我想他并不认识她。）
• I asked him if he did not know her. （我想他大约认识她。）

4.比较下面两句：

• I shall do better only if I have another chance. （我将做得好些，但必须再有一个机会。）
• I shall do better if only I have another chance. （我将做得好些，只要我再有一个机会。）

第一句可以改作I shall only do better if I have another chance。第二句可以改作I shall do better if I only have another chance。

下面两句里的If only或If ... only都从“只要…”转作“巴不得…”或“可惜不…”解：

• If only I had my life to live over again!
• If I only had come a few minutes earlier!

5.Well, well, if this (或it) isn't our old friend Mr King的意思是“这个大约就是我们的老朋友King先生。”

6.下面各句里以if引导的从句并不真正表示条件：

• If you ask my name, it is Henry Mee.
• If you wish to see my father, he is in the study.
• If you want to take a walk, there is a little garden behind the house.
• If you allow me to say so, I am afraid you are not qualified.
• We had fine weather last Friday, if you remember.

各句里的主句所说的都是客观事实，并不靠着那以if引导的从句，如第一句是“假使你问我的名字，它是Henry Mee。”其实即使“你”不问，“我”的名字还是Henry Mee。if的这种用法却是很普通的。

7.if and when是公文里的陈套语，通常用if或when就够了。

8.when or if（或when，or if，）表示这语引导的从句所说的也许不会实现。例如：I shall call on you again next week when (,) or if (,) I have a chance.

9.在以作“假使”解的if引导的从句里，虽然指将来，动词却用现在式，不用将来式，如If you see him tomorrow, give him my new address里用see不用will see。if you will see him tomorrow作“假使你明天要见他”解。

但注意下面两句：

Never use a long word if a short word will do. (if a short word will do=if, if a short word is used, it will do.)

I'll call you up at eleven this evening if that won't be too late. (if that won't be too late=if, if I call you up at eleven this evening, it won't be too late.)

10.下面各句里用虚拟现在式，现在远不及用陈述现在式普通：

• If it be (或is) fine tomorrow, we shall sail.
• If he study (或studies) harder, he will not lag behind.
• If she have (或has) already done her best, she deserves the prize.

11.在定义（definition）的开首不该用if，如不该说Home-sickness is if one longs for one's home。