if释义
conj.即使; 如果，倘若; 〈口〉是否; 假设;
n.条件，设想;
if的用法
if从句一般有三种用法
1、主将从现 （主句为一般将来时,从句为一般现在时）；
eg:If it rains(从句) ,I will stay at home（主句）.
=I will stay at home if it rains.
2、主句含有情态动词 （must、may、can etc.）从句为一般现在时；
eg:If you drive too fast ,you may have an accident.
=You may have an accident if you drive too fast
3、主句为祈使句,从句要用一般现在时态；
eg:Don't play computer games if you don't finish your homework.
备注：
1、If 于句首时中间用逗号隔开,主句后不用逗号.
2、if 可用unless(除非...) 替换.unless=if...not...
3、注意虚拟语气 主句和从句都为一般过去式
eg:If I was a bird ,I could fly.（事实我不可能是鸟）
if相关词组
if you want/like 如果你愿意的话
You can come and stay with us if you want.
if so如果是的话
Are you planning to return to work, and if so, who is going to look after the baby?
if not如果不是的话
Has anyone dealt with the technical problems? And if not, why not?
if necessary/if possible 如果必要/可能的话
We are ready to fight for our rights if necessary.
I should like to be back here by 10:30 if possible.
even if即使
I’d rather never sell this painting, even if they offered me a million dollars.
what if 要是……，那怎么办？ 如果……那会怎样？
What if the boss walked in here now and saw us?
as if好像是……
She always talks to me as if she was my sister.
if的用法例句
1、She gets very upset if I exclude her from anything
要是有什么事情我不让她参加，她会非常难过。
2、He asked if I had left with you, and I said no
他问我是否和你一块儿离开的，我说不是。
3、Sometimes, that standard is quite difficult, if not impossible, to achieve
有时即便有可能达到那个标准，那也是非常困难。
4、If I could just make another small point about the weightlifters in the Olympics
请允许我就有关奥运会举重运动员的问题再补充一点。
5、I wonder if you'd be kind enough to give us some information, please?
请问您能不能给我们提供一些信息？