很多考生在写托福作文的时候常常用到举例说明的句式，大家在举例的时候常常会这么说“如果………”,”假设………..”,即if………先不说这种举例的好还是坏,就本身的句子而言,很多都是有问题的。下面小编总结了一些if的用法，供大家参考学习。

　　先看两个例子:

　　[Scenery]Sue has lost her watch. She think it may be at Ann’s house.

　　SUE: I think I left my watch at your house. Have you seen it?

　　(1) ANN: no, but I’ll have a look when I get home. If I find it, I’ll tell  you.

　　If I find…., I’ll……

　　(2) Ann says: If I found a wallet in the street, I’d take it to the  police.

　　If I found……, I’d(=I would)……..(而不是if I find, I’ll…..)

　　这里两个句子有着不同的意思,前者表示Ann觉得她有找到手表的真实可能性.因此才说if I find….., I’ll…..

　　而后者是完全不同的情况.在这里Ann没有考虑真实的可能性;她在虚拟这一个情景,并不认为真的可以在街上拣到手表.于是才说:if I  found……,I’d……

　　if I do……….和if I did………的区别

　　用if+过去式(if I found / if you were / if we didn’t等)  表示虚拟的事情,而不是指过去时间发生的事情:

　　What would you do if you won a million pounds?

　　I don’t really want to go to their party, but I probably will go. They’d be  offended if I didn’t go

　　Sarah has decided not to apply for the job. She isn’t really qualified for  it, so she probably wouldn’t get it if she applied.

　　If从句中一般不用would:

　　I’d be very frightened if somebody pointed a gun at me.(而非if somebody would  point)

　　If I didn’t go to their party, they’d be offended(而非if I wouldn’t go)

　　If …….would可以表示用来请求某人做某事:

　　I would be grateful if you would send me your brochure as soon as  possible.

　　“Shall I close the door?” “yes, please, If you would.”

　　Would(‘d) / wouldn’t用于句子的主句(不是if从句)

　　If you took more exercise, you’d (=you would) probably feel healthier.

　　Would you mind if I used your phone?

　　I’m not tired enough to go to bed yet. I wouldn’t sleep.

　　另外,if引导的条件句也能引起倒装,如果要是在作文里用到,也是一个加分点:

　　先看正常语序.

　　It would be a serious setback, if the talks were to fail.

　　If you should need more information, please telephone our main office.

　　If Alex had asked, I would have been able to help.

　　倒装是要省略if

　　it would be a serious setback, were the talks to fail.

　　Should you need more information, please telephone our main office.

　　Had Alex asked, I would have been able to help

　　倒装句比if-从句更加正式.

　　但是在否定句里面,不可以用缩写

　　e.g.

　　Had he not resigned, we should have been forced to sack him(不用hadn’t  he…..)

　　在写托福作文的时候,希望大家举例的时候能够写实例,因为实例有它的特指性和行,当然,如果实在你没有经历过,在举例虚拟一个场景的时候,  if起头,就不要弄错了.